LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 


das* 


m 


or  THE 
UNIVERSITY 

OF 


CONCRETE-BLOCK  MANUFACTURE 


PROCESSES  AND  MACHINES 


BY 

HARMON    HOWARD    RICE 


FIRST    EDITION 
FIRST     THOUSAND 


NEW   YORK 

JOHN    WILEY    &    SONS 

LONDON:     CHAPMAN    &    HALL,     LIMITED 

1906 


•fiEfJEHAL 


Copyright,  1906 

BV 
HARMON  HOWARD  RICE 


ROBERT   DRUMMOND,    PRINTER,   NEW  YORK 


PREFACE. 


THE  object  of  this  book  is  to  present  in  a  simple  manner 
those  well-established  principles  of  concreting  which  practice 
has  shown  applicable  to  the  manufacture  of  concrete  blocks  for 
building  hollow  walls. 

The  theoretical  and  technical  questions  which  arise  in  connec- 
tion with  the  industry  are  only  considered  in  so  far  as  benefit  may 
result  to  the  operator  in  the  actual  manufacture  of  blocks  and 
their  use  in  construction. 

The  conclusions  which  have  been  reached  are  the  result  not 
only  of  the  author's  experience  in  actual  work,  but  of  a  careful 
consideration  of  the  successes  and  failures  of  a  large  number 
of  operators  throughout  a  series  of  years,  supplemented  by  a 
careful  weighing  of  the  many  articles  bearing  on  particular 
phases  of  the  subject  which  have  been  published  in  cement, 
engineering,  and  building  magazines. 

To  many  it  will  appear  that  this  book  is  unduly  critical. 
For  this  no  apology  is  offered.  As  the.  industry  grows  much  of 
the  evil  herein  criticised  will  pass  away,  and  it  is  hoped  that  this 
work  may,  in  some  measure,  aid  in  giving  to  the  weaknesses 
of  the  industry  that  prominence  which  can  alone  secure  their 
eradication,  to  the  end  that  concrete  blocks  may  universally 
attain  that  high  regard  now  accorded  in  localities  where  they 
are  manufactured  by  really  able  hands. 


152375 


vi  PREFACE. 

As  no  allusion  to  patents  is  made  in  the  text,  the  author  deems 
it  but  fair  to  here  state  that  very  many  of  the  designs 
and  machines  shown  are  protected  by  letters  patent. 

To  those  manufacturers  whose  ready  cooperation  has  been 
both  a  powerful  stimulus  and  a  substantial  aid  in  the  production 
of  this  work  grateful  acknowledgment  is  rendered.  To  those 
who  have  so  generously  furnished  illustrations  of  the  machines 
they  make,  and  of  the  buildings,  blocks,  and  special  members 
produced  in  machines  or  molds  of  their  manufacture,  the  author's 
thanks  are  due.  This  list  is  as  follows:  The  Winget  Concrete 
Machine  Co.,  Columbus,  Ohio,  Figs,  n  and  18;  The  Cement 
Working  Machinery  Co.,  Detroit,  Michigan,  Fig.  44;  Kells' 
Foundry  and  Machine  Co.,  Adrian,  Michigan,  Fig.  5;  Miracle 
Pressed  Stone  Co.,  Minneapolis,  Figs.  10,  13,  38,  and  39;  H.  S. 
Palmer  Hollow  Concrete  Building  Block  Co.,  Washington,  D.  C., 
Figs.  3,  14,  and  15;  J.  B.  Prescott  &  Son,  Webster,  Massa- 
chusetts, Fig.  40;  White  Cement  Machinery  Co.,  Jackson, 
Michigan,  Fig.  43;  The  Hayden  Automatic  Block  Machine 
Co.,  Columbus,  Ohio,  Figs.  17  and  34;  Contractors'  Supply  and 
Equipment  Co.,  Chicago,  Fig.  i;  Municipal  Engineering  Lnd 
Contracting  Co.,  Chicago,  Fig.  2;  Ideal  Concrete  Machinery 
Co.,  South  Bend,  Indiana,  Figs.  28,  30,  31,  and  35;  Simpson 
Cement  Mold  Co.,  Columbus,  Ohio,  Fig.  45;  The  American 
Hydraulic  Stone  Co.,  Denver,  Colorado,  Figs.  6,  7,  8,  9,  12,  19, 
21,  23,  24,  25,  27,  29,  32,  33,  36,  and  37;  The  Pettyjohn  Co., 
Terre  Haute,  Indiana,  Figs.  16,  22,  and  26;  Concrete  Block 
Machine  Co.,  Auburn,  Indiana,  Fig.  4;  Century  Cement  Machine 
Co.,  Rochester,  New  York,  Figs.  41  and  42;  Chase  Foundry  and 
Manufacturing  Co.,  Columbus,  Ohio,  Fig.  20.  The  frontis- 
piece is  presented  by  courtesy  of  The  Cement  Age,  New  York. 

HARMON  HOWARD  RICE. 

DENVER,  COLO.,  March  1906. 


CONTENTS. 


CHAPTER    I. 

CONCRETE. 

Definition..  


PAGE 

I 


General  theory 2 

Monolithic  construction 2 

Advantages  of  block  construction. 3 

CHAPTER    II. 

CEMENT. 

History  of  hydraulic  cements 4 

Puzzolan  cement 4 

Natural  cement 5 

Portland  cement 

Processes  of  manufacture 7 

Testing  cement ? 

CHAPTER    III. 

AGGREGATE. 

Definition 

Sand. 

Gradation  of  sizes 

Screenings 

Gravel  and  broken  stone 

Cinders 

vii 


vni  CONTENTS. 

CHAPTER   IV. 

WATER. 

PAGE 

Purity 13 

Quantity 13 

Water  in  curing 14 

In  winter  work 14 

CHAPTER    V. 

OTHER    INGREDIENTS. 

Lime 1 6 

Hydrated  lime 17 

Chemical  adulterants 1 8 

Waterproofing  compounds 1 8 

Coloring-matter 19 

CHAPTER    VI. 

PROPORTIONING. 

Methods  of  expressing 20 

Importance  of  ascertaining  local  conditions 20 

Theory  of  correct  proportions 21 

Determination  by  specific  gravity 21 

Determination  by  the  water  method 22 

Determination  by  relative  volume 22 

CHAPTER    VII. 

MIXING. 

Importance  of  thorough  manipulation 24 

Method  of  hand-mixing 25 

Power-mixing 26 

Continuous  vs.  batch  mixers 27 

CHAPTER   VIII. 

SHAPE     OF     BLOCKS. 

Advantages  of  hollow  space < .  31 

Description  of  representative  types e..  33 


CONTENTS.  ix 
CHAPTER   IX. 

PROCESSES. 

PAGE 

Classification  of  processes 43 

Hand  and  pneumatic  tamping 44 

Pouring 44 

Casting  in  sand 45 

Mechanical  pressure 46 

Hydraulic  pressure 46 

CHAPTER    X. 

PLASTICITY. 

Discussion  of  normal  consistency 48 

Dry  mixture 49 

Medium  and  wet  mixtures 50 

CHAPTER    XI. 

FACING. 

Difficulty  of  facing  in  general  concrete  work 51 

Various  methods  of  facing  blocks 52 

Colored  facing 53 

Waterproof  facing 54 

Form  of  face-plates 54 

CHAPTER   XII. 

ORNAMENTATION. 

Methods  of  producing 56 

CHAPTER    XIII. 
CURING. 

Importance 59 

Secrets  of  success 60 

Method  and  time 6 1 

Steam-curing 63 

Curing  in  winter 63 


X  CONTENTS. 

CHAPTER   XIV. 

MACHINES. 

PAGE 

Classification  of  machines 64 

Objects  of  machines 65 

Description  of  representative  machines ; . . .  66 

CHAPTER    XV. 

PLANT   ARRANGEMENT. 

Location 75 

Racks  and  cars 76 

Overhead  bins  and  conveyors 78 

Curing-yard 78 

CHAPTER    XVI. 

PLANT    EMPLOYEES. 

Foreman 80 

Mold-maker 8 1 

Modeler    82 

Common  labor 82 

Masons 82 

CHAPTER    XVII. 

VOIDS. 

Classification  of  causes 84 

Gradation  of  aggregate 84 

Mixing 85 

Adequate  matrix 85 

Condensation 85 

CHAPTER    XVIII. 

QUALITIES    OF    CONCRETE   BLOCKS. 

Soundness 87 

Strength 88 

Density 89 

Impermeability 90 


CONTENTS.  xi 

PAGE 

Fire-resistance 91 

Sound-proof 93 

Vermin-proof 94 

Ventilation 94 

Durability 94 


CHAPTER    XIX. 

TESTING     BLOCKS. 

General  neglect 95 

Philadelphia  specifications  for  complete  tests 96 

Demonstrative  tests 100 

CHAPTER    XX. 

BLOCK  USES. 

Adaptability  for  all  classes  of  buildings 101 

CHAPTER    XXI. 

CAUSES    OF    FAILURE. 

Culpable  errors  of  the  machine  manufacturers 117 

Causes  of  failure  chargeable  to  the  operators. 119 

CHAPTER    XXII. 

COST. 

Cost  analysis 121 

Method  of  computing  cost  of  materials 122 

Labor  cost 12  j 

Administration  and  incidentals 1 24 

CHAPTER    XXIII. 

ARCHITECTURE. 

Inartistic  conception  of  operators 126 

Architectural  style  susceptible  of  improvement 1 29 


xii  CONTENTS. 

CHAPTER    XXIV. 

BUILDING   CONSTRUCTION. 

PAGE 

Foundations  and  footings 13° 

Supporting  joists  and  girders 13° 

Floors 1 3 l 

Width  of  walls 1 3 1 

Partitions 131 

Nailing  to  walls I31 

Blocks  of  special  shapes 132 

Following  plans 1 33 

CHAPTER    XXV. 

BUILDING    REGULATIONS. 

Philadelphia  regulations  in  full 1 34 

Denver  regulations  in  full 138 

Synopsis  of  Minneapolis  regulations 141 

Synopsis  of  Newark  regulations 142 

General  criticism  and  suggestion 142 

CHAPTER    XXVI. 

MANUFACTURE   OF   ACCESSORIES, 

Accessory  molds , 1 45 

Method  of  making  and  using  molds 147 


ILLUSTRATIONS. 


Frontispiece,  Office  Buffington  Plant  Illinois  Steel  Co.  PAGE 

Fig.     i .  Rotary  mixer 28 

2.  Cube  mixer 28 

3.  Hollow  blocks  and  wall 29 

4.  Three- web  hollow  blocks  and  wall 32 

5.  Blocks  of  two  slabs  with  metal  ties 35 

6.  Two-piece  blocks  and  wall 37 

7.  Diagram  of  two-piece  wall ' 37 

8.  Angelus  Hotel,  El  Paso,  Texas 38 

9.  Interlocking  three-member  wall 40 

10.  Block  with  staggered  air-space 41 

1 1 .  Pneumatic  tamper  in  operation 44 

1 2.  Ornamental  work  for  power-house 57 

1 3.  Molds  and  accessories  of  roll-over  type 62 

14.  Upright  machine  with  drop  cores 65 

i  5.  Upright-machine  releasing-block 67 

1 6.  Moving  the  mold  rather  than  the  block 68 

17.  Face-down  machine 69 

1 8.  Combination  upright  and  face-down  machine 71 

19.  Mechanical  press  making  two-piece  blocks 72 

20.  Car  suitable  for  concrete  blocks 76 

2 1 .  System  of  cars  and  tracks 77 

22.  Ruins  of  Carbon,  Ind.,  fire 92 

23.  Ruins  of  Estherville  fire 93 

24.  Column  demonstrating  strength 99 

25.  Methodist  church,  McCook,  Neb 101 

xiii 


xiv  ILLUSTRATIONS. 

PAGE 

Fig.  26.  Entrance  to  Cottage  Hill  Cemetery 102 

27.  Cottage  at  Nashville,  Tenn 102 

28.  Church  at  North  Liberty,  Ind 103 

29.  Residence  at  Nashville,  Tenn 106 

30.  Residence  at  Warsaw,  Ind 107 

31.  Home  at  Port  Washington,  Wis. 109 

32.  Residence  at  Denver,  Colo 1 1 1 

33.  Warburton  Building,  Tacoma,  Wash 1 1 1 

34.  Residence  in  Columbus,  Ohio 112 

35.  Entrance  to  Fairview,  Bluffton,  Ind 113 

36.  Nebraska  State  Normal  School 115 

37.  Decorative  features  of  two-piece  wall 124 

38.  Beautiful  decoration  in  concrete  blocks 127 

39.  Ornamentation  of  a  pitch-face  wall 128 

40.  Metal  wall-plug 131 

41.  Various  shapes  and  designs 132 

42.  Variety  in  size  and  style 1 32 

43.  Cement  sill-mold „ 147 

44.  Ornamental  accessories 1 48 

45.  Porch  column  and  balustrade 149 


OF  THE 

UNIVERSITY 

OF 


CONCRETE-BLOCK  MANUFACTURE  , 
PROCESSES    AND   MACHINES. 


CHAPTER  I. 

CONCRETE. 

ONE  of  the  greatest  difficulties  encountered  in  the  introduc- 
tion of  concrete  blocks  has  been  ignorance  of  the  character  of 
concrete,  its  ingredients,  its  qualities,  its  uses,  and  its  limita- 
tions. It  is  scarcely  necessary  to  dwell  upon  the  importance 
of  this  knowledge  to  those  in  any  manner  interested  in  concrete 
blocks. 

Concrete  may  well  be  defined  as  a  hard,  stone-like  mass 
resulting  from  the  mixture  of  aggregates  of  various  nature  and 
size  with  a  cementitious  substance  possessing  sufficient  hydrau- 
licity  to  become  thoroughly  indurated  by  the  addition  of  water. 
It  will  therefore  appear  that  there  is  a  wide  range  of  variance 
as  to  the  bonding  material,  as  to  the  aggregate,  as  to  propor- 
tions and  manipulation  of  the  mass,  as  to  methods  of  conden- 
sation and  curing,  and  as  to  form,  size,  and  shape  of  the  result- 
ing construction. 

In  modern  practice  in  the  United  States,  concrete  has  been 
limited  to  the  use  of  various  aggregates  with  hydraulic  cements; 


2  CONCRETE-BLOCK  MANUFACTURE. 

and  the  aggregates  have  usually  been  limited  to  such  materials 
as  sand,  gravel,  stone,  or  cinders.  In  ordinary  concrete-block 
work,  this  limitation  is  carried  still  further,  especially  as  pro- 
hibiting the  use  of  other  than  Portland  cements. 

The  general  theory  of  concrete  involves  the  thorough  coating 
of  the  larger  particles  of  the  aggregate  with  sand  and  cement 
mortar,  and  the  coating  of  the  smaller  particles  with  neat  cement 
paste,  so  that  all  are  thoroughly  bonded  together  by  the  crystals 
formed  in  course  of  the  chemical  action  resulting  from  hydration 
of  the  cement.  It  is  therefore  apparent  that  cement  is  the  vital 
element  in  the  production  of  concrete;  that  the  quantity  of  water 
and  the  time  and  method  of  its  application  are  of  importance; 
and  that  the  qualities  of  the  concrete  are  largely  governed  by 
the  character  of  the  aggregate  and  by  its  quantity  as  related 
to  the  cement,  and  also  by  the  relative  quantities  of  the  different 
sizes  and  kinds  of  aggregate  as  related  to  each  other.  The 
mechanical  factors  of  manipulation  in  mixing,  of  methods  of 
depositing  and  compacting,  and  of  maintaining  proper  con- 
ditions to  secure  thorough  crystallization  in  the  final  set,  are 
not  of  less  value. 

The  multitudinous  uses  of  concrete  have  developed  from 
its  plasticity,  and  the  consequent  ease  with  which  it  assumes 
any  desired  form.  It  would  be  somewhat  aside  from  the  intent 
of  this  work  to  speak  of  the  uses  of  concrete  outside  of  walls 
and  the  construction  of  buildings,  especially  as  these  afford  ample 
proof  of  its  adaptability,  it  being  now  generally  utilized,  either 
plain  or  reinforced,  for  every  member  of  high-class  construction. 

From  the  dams,  reservoirs,  and  retaining-walls  of  railroad 
and  government  engineers  it  was  an  easy  step  to  monolithic 
building  construction,  and  it  is  to  its  success  that  the  develop- 
ment of  block  construction  is  due.  The  major  portion  of  the 
expense,  in  connection  with  plain  concrete  walls  built  in  place, 


CONCRETE.  3 

lies  in  the  construction  of  forms  and  the  handling  of  the  con- 
crete, while  the  difficulties  attendant  upon  securing  a  satisfac- 
tory surface  have  led  to  the  use  of  veneering  for  structures  of 
the  better  class.  To  obviate  these  difficulties,  concrete  blocks 
were  brought  forth,  which  might  be  constructed  in  factories 
equipped  with  suitably  designed  molds  and  appliances  for  manu- 
facture under  conditions  calculated  to  secure  the  best  results 
by  adherence  to  the  demands  arising  from  the  inherent  qualities 
of  concrete  in  plastic  form.  Thus  the  abnormal  expense  inci- 
dent upon  the  labor  of  taking  down  and  resetting  forms,  and 
of  depositing  the  concrete,  is  eliminated,  and  in  its  place  is  the 
small  labor  cost  of  a  well-equipped  and  thoroughly  systematized 
factory,  while  the  compacting  of  the  mass  is  greatly  facilitated 
and  the  important  item  of  curing,  entirely  absent  in  monolithic 
work,  is  a  matter  of  easy  accomplishment.  Block  manufacture 
also  opens  an  illimitable  field  in  decorative  art,  and  the  fact 
that  it  has  thus  far  fallen  into  incompetent  hands  does  not  di- 
minish the  ultimate  advantage. 

The  greatest  relative  advantage  of  concrete  blocks  lies  in 
the  use  of  shapes  resulting  in  hollow  walls;  and  it  may  hereafter 
be  understood  that  any  reference  to  concrete  blocks,  not  other- 
wise specifically  qualified,  shall  be  taken  to  mean  either  blocks 
containing  one  or  more  hollow  spaces  or  blocks  of  such  shape 
that  their  combination  in  a  wall  will  produce  hollow  spaces 
therein. 


CHAPTER  II. 

CEMENT. 

THE  history  of  hydraulic  cements  is  a  matter  of  great  an- 
tiquity, as  some  combination  of  materials  properly  classed  under 
this  heading  was  evidently  known  to  the  ancient  Egyptians,  and 
employed  by  them  in  the  massive  structures  testifying  to  their 
genius  in  structural  engineering. 

It  is,  however,  more  customary  to  date  the  discovery  of  the 
principle  of  hydraulic  cements  from  the  time  that  the  Romans 
mixed  puzzolana  with  lime,  and  demonstrated  that  a  mixture 
of  burned  clay  and  lime  resulted  in  a  material  which  would 
crystallize,  or  set,  upon  the  application  of  water.  This  fact  is 
so  well  authenticated  that  when,  after  a  lapse  of  centuries,  Mr. 
James  Parker  discovered  in  the  Isle  of  Sheppey  natural  materials 
of  composition  suitable  for  the  production  of  hydraulic  cement, 
that  cement  came  to  be  called  Parker's  or  Roman  cement.  The 
development  of  the  Portland  cement  industry  followed  as  the 
attention  of  engineers  was  drawn  to  its  possibilities,  and  as  chem- 
ists discovered  the  requisite  constituents  and  the  natural  mate- 
rials in  which  those  elements  occur  in  form  most  available  for 
cement  manufacture. 

Puzzolan  cement  derives  its  name  from  the  ancient  cement 
of  the  Romans.  It  properly  includes  cement  made  by  grinding 
together,  without  subsequent  calcination,  a  mixture  of  hydrated 
lime  and  such  other  material  as  slag,  burned  clay,  or  trass  obtained 
from  volcanic  tufa.  In  American  practice,  however,  the  ingre- 
dients of  Puzzolan  cement  are  limited  to  hydrated  lime  and 

4 


CEMENT.  5 

granulated  blast-furnace  slag.  It  is  no  longer  called  "  slag 
cement,"  for  the  reason  that,  in  the  manufacture  of  certain  brands 
of  true  Portland  cement,  furnace-slag  is  used  as  a  hydraulic  base. 
The  point  to  be  borne  in  mind  in  reference  to  Puzzolan-cement 
manufacture  is  that  the  materials  are  not  calcined  after  mixing. 
They  are,  however,  ground  to  extreme  fineness,  and,  as  the  lime 
is  prehydrated,  but  little  water  is  required  in  mixing  concrete. 
Puzzolan  cement  is  of  a  light-lilac  color,  of  a  lower  specific  gravity 
than  Portland,  and  the  presence  of  sulphides  produces  a  green 
color  in  the  fracture  of  a  pat  which  has  been  long  under  water. 
While  its  tensile  strength  may  approximate  that  of  Portland, 
its  strength  under  compression  is  much  less.  It  is  not  suitable 
for  any  use  in  dry  places  or  above  ground,  as  oxidation  results 
in  cracks  and  disintegration;  and  it  is  therefore  evident  that, 
for  the  ordinary  service  demanded  of  concrete  blocks,  it  is  mani- 
festly unfit. 

Natural  cement  is,  as  its  name  implies,  produced  from  natu- 
ral cement  rock  found  in  various  sections  of  the  United  States, 
and  is  the  same  as  the  Roman  cement  of  England.  The  analyses 
of  cement  rock  vary  greatly  in  different  localities,  and  even  in 
adjoining  sections  in  the  same  district.  In  some  cases  it  approxi- 
mates rather  closely  the  requirements  of  the  raw  materials  for 
Portland-cement  manufacture,  while  in  some  factories  two  or 
more  kinds  of  rock  are  mixed,  but  without  that  definite  chemical 
analysis  obtaining  in  the  manufacture  of  Portland.  The  process 
of  manufacturing  natural  cement  does  not  involve  so  high  a 
temperature  in  the  kiln  as  in  the  case  of  Portland,  the  calcina- 
tion merely  sufficing  to  liberate  the  carbonic-acid  gas.  Con- 
sequently the  clinker  is  more  easily  ground;  and  for  this  pur- 
pose burr-stones  were  formerly  universally  employed,  although 
some  factories  have  recently  installed  grinding-machinery  of 
similar  type  to  that  used  in  Portland  mills.  Natural  cement 


6  CONCRETE-BLOCK  MANUFACTURE. 

is  well  adapted  for  use  in  the  interior  of  heavy  masonry,  where 
the  concrete  will  not  be  subject  to  attrition  or  blows;  but  good 
practice  demands  that  a  larger  proportion  be  used  than  would 
be  required  of  Portland,  and  'the  question  of  determination  as 
between  the  use  of  the  two  becomes,  in  such  cases,  an  economic 
problem.  It  is  apparent  that  it  is  not  suited  for  concrete-block 
work,  as  the  severe  service  demanded  of  the  blocks  in  general 
construction,  and  the  desirability  of  providing  a  large  hollow 
space  by  making  face-sections  as  thin  as  consistent  with  safety, 
requires  a  cement  beyond  possible  criticism  or  doubt. 

Portland  cement  is  produced  by  intimately  mixing  or  grind- 
ing together  definite  proportions  of  argillaceous  and  calcareous 
substances,  usually  75%  of  the  former  and  25%  of  the  latter, 
burning  this  material  to  semifusion  and  grinding  the  resultant 
clinker  to  an  impalpable  powder.  The  features  which  distinguish 
Portland  cement  from  all  other  cements  are  the  intense  heat 
at  which  the  pulverized  raw  materials  are  calcined,  and  the  accu- 
rate proportioning  of  the  essential  elements  entering  into  its 
composition.  These  elements  are  lime,  silica,  alumina,  and 
oxide  of  iron,  and  there  must  be  in  the  finished  product  not  less 
than  1.7  times  as  much  lime  by  weight  as  of  the  other  elements 
mentioned.  These  elements  are  found  in  various  materials,  and 
the  following  classification  includes  all  raw  materials  commonly 
employed  : 

CALCAREOUS  MATERIALS.        ARGILLACEOUS  MATERIALS. 
Limestone.  Cement  Rock. 

Marl.  Clay. 

Chalk.  Shale. 

Slag. 

The  raw  materials  were  formerly  ground  between  burr- stones, 
which  have  been  generally  replaced  by  ball-  and  tube-mills, 


CEMENT.  7 

Griffin  or  Kent  mills.  The  grinding  of  the  materials  to  extreme 
fineness  before  calcination  is  one  of  the  greatest  factors  in  suc- 
cessful cement  manufacture;  and  in  this  connection,  as  well  as 
in  the  grinding  of  the  clinker,  the  Griffin  mill,  which  operates 
on  a  principle  similar  to  a  gyratory  crusher,  has  been  a  distinct 
factor  in  the  development  of  the  Portland-cement  industry. 
After  grinding,  the  material  is  again  sampled  and  chemical 
analysis  made.  When  the  prescribed  proportions  have  been 
obtained,  the  material  is  fed  into  a  long  rotary  kiln,  into  the 
lower  end  of  which  the  fuel  is  introduced.  The  revolutions  of 
this  kiln,  the  injection  of  fuel  and  the  feeding  of  the  charge  being 
under  the  direct  control  of  the  operator,  insures  a  product  of 
such  uniform  excellence  as  could  not  be  approached  under  the 
burning  in  intermittent  dome- kilns  or  continuous  vertical  kilns 
formerly  in  vogue.  Indeed,  it  may  be  said  that  to  the  rotary 
kiln,  more  than  to  all  else,  is  due  the  remarkable  growth  in  the 
manufacture  of  American  Portland  cements,  the  increase  in 
their  quality  and  uniformity  and  the  decrease  in  their  cost.  From 
these  long  kilns  the  clinker  is  delivered  in  particles  about  the 
size  of  peas ;  and  it  is  a  fact  worthy  of  notice  that  these  particles 
are  inert,  for  it  accentuates  the  later  observation  that  the  hydrau- 
licity  of  cement  increases  with  fineness  of  grinding.  By  means 
of  grinding-machinery  already  mentioned,  this  intensely  hard 
clinker  is  reduced  to  the  Portland  cement  of  commerce. 

The  wet  process  formerly  differed  radically  from  the  dry, 
and  involved  the  formation  of  slurry  bricks,  which  were  then 
introduced  into  kilns  of  a  style  no  longer  in  use.  At  the  present 
time,  however,  the  difference  between  the  two  processes  in  the 
United  States  only  involves  mixture  of  marl  and  pulverized  clay 
in  pug-mills  or  edge-runners,  with  subsequent  grinding  in  wet 
tube-mills,  after  which  the  process  is  continued  as  already 
described. 


CONCRETE-BLOCK  MANUFACTURE. 

The  extreme  care  exercised  in  the  manufacture  of  standard 
brands  of  American  Portland  cements,  the  large  number  of 
factories  operating  in  all  sections  of  the  country,  the  enormous 
increase  in  production  and  consumption  of  the  product  and 
its  satisfactory  use  in  the  most  important  work  of  government 
and  railroad  engineers,  leave  no  room  for  doubt  as  to  its  adapta- 
bility for  the  highest  class  of  concrete-block  construction,  and 
afford  no  excuse  to  those  who  refuse  to  abandon  the  prejudice 
which  favored  European  brands  in  the  days  of  the  infancy  of 
this  great  American  industry. 

Of  the  standard  tests  for  cement,  that  of  greatest  importance 
to  the  concrete-block  manufacturer  is  the  test  for  constancy 
of  volume;  and  it  especially  commends  itself  because  requiring 
no  apparatus  other  than  a  glass  molding-board  and  pieces  of 
glass  on  which  the  pats  may  remain  during  the  period  of  test. 
Circular  pats  should  be  formed  three  inches  in  diameter,  a  half 
inch  thick  at  the  center  and  tapering  toward  the  edge.  After 
remaining  in  thoroughly  moist  air  for  twenty-four  hours,  one  should 
be  steamed  for  about  four  hours.  This  is  called  an  accelerated 
test,  and  tends  to  quickly  develop  any  imperfections.  It  is  usual 
to  specify  that,  in  case  of  failure  in  the  accelerated  test,  the  cement 
may  be  again  tested  twenty-eight  days  later,  as  it  may  withstand 
this  severe  test  when  properly  aged.  Another  pat  should  be 
exposed  in  moist  air,  and  still  another  immersed  in  water,  results 
being  noted  in  the  latter  two  cases  at  intervals  during  twenty- 
eight  days.  If  the  cement  be  sound,  it  should  not  disintegrate, 
or  show  expansion  cracks  in  the  edge  of  the  pat.  A  slight  curling 
of  the  edge  is  not  harmful  in  the  air  specimen,  but  should  not 
occur  in  one  immersed  in  water.  Shrinkage  cracks  on  the  cen- 
ter and  hair  cracks  on  the  surface  are  commonly,  in  neat  cement- 
work,  the  result  of  careless  manipulation,  excess  of  water,  or 
too  rapid  drying,  and  may  be  disregarded  in  the  test. 


CHAPTER  III. 

AGGREGATE. 

THE  inert  coarse  material  which,  in  combination  with  cement 
and  water,  produces  concrete  is  termed  the  aggregate,  and  is 
divisible  into  fine  aggregate  of  sand  or  stone  screenings  and 
coarse  aggregate  of  gravel,  broken  stone,  or  cinders. 

The  mineralogy  of  sand  has  but  slight  effect  upon  its  com- 
bination with  cement,  and  the  best  authorities  consider  it  of. 
so  much  less  importance  than  the  physical  properties  that  it 
may  safely  be  passed  without  discussion. 

The  shape  of  grain  has  been  carefully  considered,  and  while 
some  tests  appear  to  show  as  great  strength  in  round  grains  as 
in  sharp,  and  while  satisfactory  work  has  been  done  with  sand 
of  rounded  grains,  the  best  engineers  continue  to  specify  that 
sand  shall  be  sharp.  Where  local  conditions  admit  of  choice 
between  the  two,  the  sharp  sand  should,  other  qualities  being 
equal,  invariably  be  selected.  The  strength  and  firmness  of  the 
grains  is  an  item  of  much  importance;  and  perhaps  the  best 
method  of  choosing  sand  is  to  determine  its  firmness  and  grit 
by  rolling  in  the  palm  of  the  hand  or  between  the  fingers,  mean- 
while applying  considerable  pressure.  Another  excellent  method 
is  to  test  the  sand  for  absorption.  This  cannot  be  accomplished 
in  the  manner  of  usual  percentage  tests,  as  the  capillary  attrac- 
tion between  grains  will  take  up  a  considerable  amount  of  water, 
even  though  the  sand  be  practically  non-absorbent.  The  proper 

9 


10  CONCRETE-BLOCK  MANUFACTURE. 

way  is  to  let  the  sand  soak  for  an  hour,  and  then  examine  it  in 
the  manner  already  mentioned  for  firmness  and  grit.  A  sand 
which  shows  the  slightest  tendency  to  dissolve  or  soften  under 
such  treatment  should  be  discarded. 

The  sand  should  be  clean,  and  free  from  foreign  matter  of 
every  kind.  In  general  concrete  work  there  has  been  a  dis- 
agreement among  engineers  as  to  the  permissibility  of  a  certain 
percentage  of  loam  or  clay,  and  some  have  claimed  that  it  increased 
the  strength  of  the  concrete.  A  careful  consideration  of  such 
reports,  supplemented  by  exhaustive  tests,  has  established  the 
fact  that  such  reported  increase  in  strength  only  obtains  in  lean 
concrete  of  porous  texture  in  which  the  voids  are  not  properly 
filled,  and  that,  in  every  case  of  reasonably  rich  concrete  of  such 
density  as  required  in  concrete  blocks,  strength  is  lost  by  such 
admixture.  The  object  of  this  work  is  to  raise  the  quality  of 
concrete  blocks  in  every  possible  manner,  and  it  is  therefore 
recommended  to  every  concrete-block  maker  that  sand,  which 
in  its  natural  condition  contains  any  foreign  matter,  be  washed 
until  the  water  is  no  longer  discolored. 

The  most  important  consideration  in  connection  with  the 
selection  of  sand  is  the  size  and  gradation  of  sizes.  In  this 
respect  the  inexperienced  block-maker  often  commits  grave 
error  by  the  selection  of  fine  sand,  erroneously  supposing  that 
it  contains  a  smaller  percentage  of  voids,  and  hence  hoping  to 
obtain  greater  strength  by  use  of  stated  proportions.  As  a  mat- 
ter of  fact,  the  percentage  of  solids  in  a  perfectly  dry  mixture 
of  fine  and  coarse  sand,  both  shaken  to  refusal,  is  approximately 
the  same,  and  any  difference  is  due  merely  to  shape  of  grain; 
but,  upon  the  addition  of  water,  the  volume  of  the  fine  sand 
increases  in  greater  ratio  than  the  coarse,  because  there  are 
more  grains  between  which  the  water  is  introduced,  and  there- 
fore a  fine  sand  becomes  distinctly  more  porous  than  a  coars£ 


AGGREGATE.  H 

sand.  In  the  same  manner  it  will  be  seen  that,  by  mixing  cement- 
paste  with  sand  until  every  grain  is  thoroughly  coated,  a  much 
greater  proportion  will  be  required  for  fine  sand  than  for  coarse. 
The  best  results  are  obtained  by  mixing  coarse  and  fine  sand 
in  such  sizes  and  proportions  that  the  finer  grains  tend  toward 
filling  the  voids  in  the  coarse  sand,  thus  securing  a  maximum 
density  with  a  minimum  quantity  of  cement. 

It  has  been  stated  by  eminent  authorities  that  crusher  screen- 
ings give  greater  strength  than  natural  sand,  and  tests  have 
generally  shown  results  in  accordance  with  this  statement  where 
the  stone  from  which  the  screenings  came  was  of  proper  texture. 
This  doubtless  results  from  the  variation  in  the  size  of  screen- 
ings, which  are  not  nearly  so  uniform  in  size  as  are  the  grains 
of  the  average  natural  sand,  and  thus  the  screenings  accom- 
plish to  a  certain  extent  the  same  result  obtained  by  a  careful 
mixing  of  graded  sand. 

For  the  coarse  material  of  the  aggregate,  gravel  is  commonly 
used  where  locally  obtainable  at  a  reasonable  price.  It  should 
run  in  size  from  a  quarter  inch  to  as  large  pieces  as  can  be  con- 
veniently accommodated  in  the  block  mold.  Usually  from 
I"  to  i"  should  be  the  maximum  for  concrete-block  manu- 
facture, and  the  principles  of  gradation  already  stated  for  sand 
must  be  observed  in  the  use  of  gravel.  A  great  deal  of  time 
has  been  spent  in  discussing  the  relative  merits  of  gravel  and 
broken  stone,  and  tests  appear  to  show  greater  strength  on  short- 
time  tests  of  stone  concrete  than  of  gravel  concrete,  while  tests 
extending  over  long  periods  of  time  show  little  difference.  It  is 
questionable  whether  the  results  of  such  tests  may  not  be  influ- 
enced by  considerations  other  than  the  mere  use  of  gravel  or 
stone,  such  as  the  relative  sizes  of  aggregate  or  hardness  of  the 
stone  used. 

It  must  be  remembered,  in  employing  broken  stone  as  a 


12  CONCRETE-BLOCK  MANUFACTURE. 

concrete-block  aggregate,  that  concrete  will  not  possess  strength 
in  excess  of  that  of  its  aggregate,  and  hence  soft  sandstones  or 
the  softer  limestone  formations  should  not  be  used.  A  hard 
limestone,  however,  is  a  very  desirable  aggregate,  and  is  largely 
employed  in  general  concrete  work  by  railroad  engineers.  Con- 
glomerate rock  makes  good  concrete,  while  granite  and  trap-rock 
are  the  best  that  can  be  obtained. 

Cinder  concrete  has  often  resulted  in  failure,  and,  while  its 
light  weight  commends  it  for  partition- walls,  its  use  cannot  be 
generally  recommended,  and  never  in  any  place  where  its  failure 
would  jeopardize  the  integrity  of  other  members  of  the  building. 


CHAPTER  IV. 

WATER. 

WATER  is  the  chemical  agent  which  unites  with  the  cement, 
and  results  in  that  crystallization  of  the  silicates  which  is  com- 
monly known  as  the  setting  of  the  cement.  Both  in  the  initial 
and  final  sets,  there  are  certain  scientific  principles  relative  to 
the  application  of  water  which  have  been  abundantly  demon- 
strated in  actual  practice. 

The  first  consideration  is  pure  water.  Neither  muddy  water, 
stagnant  water,  water  impregnated  with  alkali,  nor  water  dis- 
colored by  the  refuse  from  factories,  sewers,  reduction-works, 
or  the  like,  will  give  the  best  results.  The  matter  of  water,  both 
pure  and  clean,  has  been  generally  disregarded;  but  it  is  of  so 
great  importance  as  to  justify  consideration  in  the  location  of  a 
plant,  as  well  as  some  expense  in  its  equipment. 

The  quantity,  method,  and  time  of  applying  water  has  been 
grossly  disregarded,  and  it  is  to  the  haphazard  methods  of  using 
water  that  much  of  concrete-block  failure  is  justly  chargeable, 
It  is  impossible  to  overestimate  the  importance  of  using  in  the 
mix  an  amount  of  water  sufficient  to  reduce  the  cement  to  such 
plasticity  that,  with  reasonable  manipulation,  it  will  thoroughly 
coat  the  particles  of  the  aggregate.  No  good  concrete  can  be 
produced  in  any  other  manner;  and  it  is  a  fact  worthy  of  note 
that  concrete  engineers  have  generally  abandoned  the  dry  mix- 
is 


14  CONCRETE-BLOCK  MANUFACTURE. 

ture  of  bygone  days,  and  the  old  specification  of  a  "  damp- earth  " 
consistency  is  now  universally  replaced  by  a  "quaking  "  mix- 
ture. The  application  of  water  should  always  be  in  a  manner 
which  will  not  wash  the  cement  from  the  aggregate;  and  the 
quantity  should  not  be  so  copious  as  to  cause  decomposition 
by  "  drowning  "  of  the  cement,  or  to  cause  hair-cracks  by  flush- 
ing neat  cement  to  the  surface. 

Relative  to  the  matter  of  curing,  it  may  be  here  noted  that 
concrete  blocks  possess  a  distinct  advantage  in  the  opportunity 
offered  of  thorough  induration  before  going  into  the  wall.  Many 
feel  that  the  hardening  of  a  block  after  making  is  a  matter  requir- 
ing no  thought  and  no  skill.  It  is  in  reality  the  critical  time 
in  the  making  of  a  block;  and  the  best  thought  of  the  manufac- 
turer of  blocks  may  well  be  given  to  the  details  of  method,  time, 
and  quantity  in  relation  to  the  application  of  water  to  the  blocks 
after  they  come  from  the  molds,  and  before  they  leave  the  curing- 
yard. 

In  winter  work,  the  mixing-water  is  often  heated  and  results 
are  very  satisfactory,  especially  if  the  aggregate  also  be  heated. 
It  is,  of  course,  evident  that  the  time  allowed  for  setting  of  the 
cement  before  suspension  by  freezing  is  thus  greatly  lengthened, 
while  it  has  been  amply  demonstrated  that  crystallization  is 
accelerated  by  the  use  of  hot  water.  However,  under  ordinary 
conditions  of  operating  a  block-machine  in  a  closed  building 
where  the  sand- bins  are  sufficiently  warmed  by  artificial  heat 
to  drive  out  the  frost,  it  is  scarcely  necessary  to  incur  the  extra 
expense  of  heating  water. 

In  freezing  weather,  salt  is  often  added  to  the  water  used  in 
mixing  concrete,  and  the  use  of  a  reasonable  amount  causes  no 
loss  in  strength.  Various  formulas  have  been  devised  in  the 
nature  of  a  sliding-scale  based  on  the  registered  temperature, 
but  none  of  these  appear  to  be  of  great  practical  value.  All  are 


WATER.  15 

based  upon  a  certain  percentage  of  the  water  by  weight.  It  is 
evident  that,  by  the  common  rule  of  using  i%  of  salt  for  each 
degree  registered  below  32°  F.,  the  quantity  would,  in  zero 
weather,  be  excessive.  Tests  have  shown  that  10%  of  salt  is 
not  injurious. 


CHAPTER  V. 

OTHER  INGREDIENTS. 

VARIOUS  other  ingredients  are  used  by  certain  block-makers 
in  addition  to  those  mentioned  in  preceding  chapters.  In  gen- 
eral, it  may  be  said  that  the  admixture  of  any  other  substances 
should  be  regarded  as  adulterations  and  viewed  with  suspicion 
until  tests  and  actual  service  have  demonstrated  not  merely 
usefulness  for  a  specified  purpose,  but  the  fact  that  no  deleterious 
action  on  the  cement  results,  as  well  as  the  permanence  of  the 
added  material  in  relation  to  the  life  of  the  cement. 

The  use  of  lime  in  concrete  blocks  has  of  late  received  much 
attention.  It  is  well  known  that  unslaked  lime  is  eminently 
unfitted  for  such  use,  as  hydration  greatly  increases  its  bulk, 
and  hence  only  slaked  lime  has  been  employed.  There  are, 
however,  unslaked  particles  in  every  lime-bed,  and,  even  though, 
as  in  Germany,  the  lime  be  allowed  to  slake  for  months  before 
using,  this  criticism  remains  true  to  a  greater  or  less  degree.  It 
is  evident  that,  with  the  thorough  mixing  of  well-made  con- 
crete and  with  the  subsequent  saturation  of  the  block  during 
the  period  of  induration,  any  such  particles  are  liable  to  cause 
trouble  by  swelling,  producing  expansion  cracks,  and  resulting 
in  possible  failure  of  the  member  through  disintegration. 

The  block-makers  favoring  the  use  of  lime  have  therefore 
adopted  the  slaked  and  sifted  powder  offered  commercially 

16 


OTHER  INGREDIENTS.  i? 

under  the  name  of  "  hydrated  lime."  Being  comparatively  new 
as  a  commercial  product,  it  is  difficult  to  say  what  may  be  con- 
sidered as  standard  practice  in  its  manufacture.  There  appear 
to  be  two  principal  methods  in  use.  The  first  consists  in  the 
use  of  a  hooded  pan-mixer  into  which  the  lime,  previously  broken 
in  a  crusher  or  gound  in  a  tube-mill,  is  fed,  and,  as  the  mixer 
revolves  and  the  water  is  supplied  by  automatic  sprayer,  the 
mass  is  thoroughly  agitated  by  paddles,  reducing  the  slaked  lime 
to  powder,  which  is  afterward  screened,  the  screens  often  being 
as  fine  as  those  used  in  cement-testing.  The  second  process 
involves  the  use  of  a  rotary  cylinder  of  design  somewhat  simi- 
lar to  the  kilns  used  in  cement  manufacture,  the  moisture  being 
supplied  by  a  perforated  steam-pipe  forming  the  axis,  and  the 
slaked  lime  passing  through  graduated  screens,  so  that  it  can- 
not pass  a  given  section  of  the  cylinder  until  the  required  fine- 
ness be  attained.  It  is  therefore  evident  that  this  thorough 
process  of  hydration  and  pulverization  leaves  nothing  to  be 
feared,  except  that  the  life  of  the  lime  is  less  than  that  of  the 
cement.  Even  this  doubt  seems  unwarranted,  in  view  of  the 
extreme  fineness  of  the  particles,  and  the  fact  that,  although 
there  may  be  a  slight  chemical  action  between  the  lime  and 
cement,  the  latter  hypothesis  is  not  well  established,  and 
lime  is  employed  merely  on  account  of  its  capacity  for  filling 
voids.  In  this  respect  it  has  shown  great  merit,  both  in  the 
increase  of  water- tightness  and  in  greater  strength  of  lean  con- 
crete. It  is,  of  course,  evident  that  hydrated  lime  is  of  distinctly 
less  value  in  a  rich  and  carefully  graded  concrete,  in  which  the 
voids  are  well  filled,  than  it  is  in  a  lean  and  porous  concrete. 
In  the  latter  it  becomes,  unquestionably,  an  agent  for  good,  both 
as  to  density  and  compressive  strength,  unless  the  ease  of  filling 
voids  by  its  use  tempt  the  block-maker  to  carelessness  in  grada- 
tion of  aggregate,  to  an  unwise  economy  in  the  proportion  of 


1 8  CONCRETE-BLOCK  MANUFACTURE. 

cement,  and  to  the  use  of  an  unreasonably  large  proportion  of 
slaked  lime.  Ordinarily  the  amount  of  cement  by  weight  should 
be  at  least  four  times  that  of  hydrated  lime. 

It  has  been  too  customary  in  the  earlier  stages  of  the  industry 
for  block-makers  to  modify  the  natural  action  and  qualities  of 
cement  by  the  addition  of  various  chemicals.  It  may  be  set 
down  as  a  general  rule  that  all  such  adulteration  violates  funda- 
mental principles  of  good  practice,  for  the  reason  that  the  com- 
position of  standard  brands  of  American  Portland  cements  is 
determined  by  the  most  careful  chemical  analysis,  and  the  for- 
mulas, after  the  most  exhaustive  experimentation,  have  been 
prepared  with  the  object  of  producing  cement  which  shall  meet 
the  requirements  of  those  tests  specified  by  the  American  Society 
of  Civil  Engineers  and  the  American  Society  for  Testing  Mate- 
rials. Gradually  are  the  operators  of  block-machines  learning 
that  no  adulteration  can  secure  an  ultimate  gain  in  strength,  and 
that  the  gain  in  ease  of  manipulation  which  may  result  from  a 
change  in  the  normal  time  of  setting  is  no  adequate  compensa- 
tion for  jeopardizing  the  permanent  strength  of  an  otherwise 
durable  building  material. 

Of  the  various  benefits  which  have  been  claimed  for  the 
addition  of  chemicals,  perhaps  water-tightness  is  the  most  com- 
mon, both  as  to  known  chemicals  and  as  to  compounds  of  unknown 
ingredients.  It  may  be  said,  to  the  credit  of  a  large  number  of 
operators,  that  they  prefer  the  additional  labor  and  care  necessary 
to  produce  an  impermeable  block  by  natural  methods,  rather 
than  the  easier  way  of  securing  similar  results,  but  short-lived 
blocks,  by  chemical  admixture  to  a  poorly  graded  and  carelessly 
manipulated  mixture. 

The  addition  of  various  materials  for  coloring  purposes  has 
been  considered,  by  nearly  every  writer  upon  concrete  blocks 
or  concrete  building  construction  in  any  other  form,  a  matter 


OTHER  INGREDIENTS.  19 

of  sufficient  importance  to  justify  a  tabulated  statement  of  sub- 
stances and  quantities  suitable  for  producing  different  colors. 
Superficial  study  of  such  tables  will  show  a  discrepancy  so  marked 
that  their  worthlessness  for  practical  purposes  becomes  apparent. 
It  is  evident  that  any  such  table  can  only  be  applicable  to  a  par- 
ticular aggregate,  and  that  a  change  in  local  materials  will  necessi- 
tate an  entire  readjustment  of  quantities.  It  is  particularly 
noticeable  that  each  one  advocates  one  or  more  of  the  coloring 
materials  as  harmless,  while  another  author  is  equally  sure  of 
deteriorating  influence.  The  fact  is  that  every  one  of  these 
artificial  colors  causes  loss  of  strength.  To  be  sure,  other  things 
than  strength  require  consideration,  and  a  customer  may  in  rare 
cases  be  willing  to  waive  slight  reduction  in  strength  and  dura- 
bility to  attain  certain  artistic  color-effects.  If  it  becomes  necessary 
to  employ  artificial  colors,  it  is  a  wise  course  to  procure  them 
from  a  reputable  concern  whose  energies  are ,  entirely  devoted 
to  the  production  of  mineral  colors  for  concrete  under  the  most 
favorable  conditions.  Every  effort  should  be  used  to  obtain 
for  the  aggregate  crushed  rock  of  the  required  color,  as  in  this 
manner  it  is  possible  to  produce  blocks  of  any  color  which  a 
reasonable  customer  may  demand,  and  the  purity,  strength, 
and  durability  of  the  concrete  is  in  no  wise  impaired,  while  the 
blocks  are  saved  from  that  artificial  and  plaster-like  appearance 
which  too  often  obtains  in  colored  work.  Most  operators  have 
not  yet  learned  that  the  sensible  place  to  regulate  color  is  in  the 
selection  of  aggregate. 


CHAPTER  VI. 

PROPORTIONING. 

BY  the  usual  method  of  expressing  proportions  in  cement 
work,  1:4  represents  one  part  cement  to  four  parts  sand;  while 
1:2:4  represents  one  part  cement,  two  parts  sand  or  screen- 
ings, and  four  parts  gravel  or  broken  stone. 

The  relative  proportions  requisite  to  secure  the  greatest  density, 
strength,  and  impermeability — in  short,  to  make  the  best  con- 
crete blocks — are  not  the  same  in  various  localities  because  of 
the  diversity  in  locally  available  materials.  It  has  been  the 
custom  of  most  manufacturers  of  machines  to  adopt  an  arbitrary 
standard  of  proportions,  based  upon  the  results  of  their  own 
tests  and  experiments;  and,  while  these  proportions  have  been 
substantially  correct  for  a  particular  class  of  materials,  it  by 
no  means  follows  that  they  are  correct  for  other  classes  available 
in  different  localities.  It  has  often  been  the  case  that  an  operator, 
closely  following  the  advice  of  his  machinery  salesman,  has  pro- 
duced very  bad  blocks  from  very  good  material,  and  has  either 
failed  utterly  or  learned  by  experience  that  the  conditions  under 
which  he  worked  demanded  a  local  remedy. 

The  importance  of  ascertaining  correct  proportions  for  the 
particular  materials  in  use  cannot  be  overestimated,  and  all 
block-makers  should  have  the  correct  proportions  of  the  mate- 
rials they  purpose  using  determined  by  expert  tests.  The  expense 
of  such  tests  is  really  an  economy,  as  the  result  is  such  careful 

20 


PROPOR  TIONING.  2 1 

gradation  of  the  aggregate  that  maximum  quality  is  secured 
with  a  minimum  quantity  of  cement.  As  many  will  not,  however, 
be  able  or  willing  to  avail  themselves  of  such  expert  tests,  some 
elementary  methods  of  determining  proportions  may  be  helpful. 

Proportioning  involves  primarily  the  use  of  the  greatest  pos- 
sible quantity  of  as  large  aggregate  as  can  readily  be  manipulated 
in  the  particular  type  of  machine  in  use,  and  the  addition  of  a 
series  of  smaller  sizes  of  aggregate  in  quantities  sufficient  to  fill 
the  spaces  between  the  pieces  of  each  successive  larger  size  of 
aggregate.  As  each  piece  of  the  aggregate  must  be  coated  with 
cement-paste,  or  with  sand  and  cement  mortar,  it  is  evident  that 
filling  the  spaces  between  pieces  of  large-size  aggregate  with 
fine  sand  involves  the  use  of  an  unnecessary  amount  of  cement. 
It  is  equally  clear  that,  if  the  smaller  aggregate  be  too  large  for 
its  intended  purpose,  or  used  in  too  great  quantity,  the  larger 
aggregate  is  forced  apart.  In  either  case  a  loss  of  strength  or  a 
waste  of  cement  results.  It  is  clear  that  this  gradation  may  be 
continued  indefinitely,  and  that  any  attempt  to  determine  pro- 
portions of  a  mixed  aggregate  can  give  no  definite  information 
unless  the  aggregate  be  screened  until  each  sample  is  within 
such  range  of  screen  as  to  be  of  practically  uniform  size.  The 
matter  is  then  resolved  into  determination  of  voids  in  the  larger 
size  which  may  be  filled  by  the  smaller  size.  In  practice,  the 
impossibility  of  securing  an  absolutely  ideal  mixture  of  mate- 
rials has  led  to  the  customary  addition  of  5%  to  the  determined 
amount  of  sand  or  screenings,  and  10%  to  the  determined  amount 
of  cement. 

Specific  gravity  affords  an  accurate  method  of  determining 
the  percentage  of  voids,  and  the  consequent  amount  of  material 
required  to  fill  them.  As  obtaining  the  specific  gravity  of 
a  particular  substance  requires  apparatus  not  usually  found 
in  a  concrete-block  factory,  the  technical  part  of  this  test  may 


22  CONCRETE-BLOCK  MANUFACTURE. 

be  dispensed  with  by  assuming  the  weight  of  a  solid  and  unbroken 
cubic  foot  of  sandstone  to  be  150  Ibs.,  of  trap-rock  180  Ibs.,  and 
other  stone  of  intermediate  weights,  while  sand  and  gravel  may 
be  safely  estimated  at  165  Ibs.  The  aggregate  of  which  it  is 
desired  to  determine  the  voids  should  be  dried  to  a  constant 
weight,  and  shaken  to  that  degree  of  compactness  which  it  is 
expected  to  attain  in  the  finished  block.  By  subtracting  the 
weight  of  a  cubic  foot  of  the  aggregate  in  this  condition  from 
the  weight  of  a  solid  cubic  foot,  as  above  estimated,  and  divid- 
ing the  remainder  by  the  weight  of  a  solid  cubic  foot,  the  result 
will  be  the  percentage  of  voids. 

Another  method  commonly  employed,  but  less  accurate,  is 
that  of  pouring  a  measured  quantity  of  water  into  the  aggregate, 
and  determining  the  percentage  existing  between  the  measure 
of  aggregate  and  the  measure  of  water.  It  is  evident  that  if 
the  aggregate  be  dry  it  will  absorb  a  certain  percentage  of  the 
water,  and  if  it  be  wet  the  particles  are  separated  by  water  ten- 
sion. It  is  a  speedy  method  where  hasty  determination  is  necessary, 
but  should  always  be  considered  approximate,  and  subject  to 
verification  by  more  accurate  methods. 

Determination  by  relative  volume  is  doubtless  the  most  prac- 
tical method  of  proportioning,  and  is  of  especial  value  when 
used  as  a  check  upon  the  last-mentioned  test.  A  known  weight 
of  dry-mixed  aggregate  and  cement  in  supposedly  correct  pro- 
portions is  placed  in  a  vessel,  shaken  to  refusal,  and  the  height 
marked.  Equal  weights  of  slightly  different  mixtures  are  then 
deposited  in  the  vessel  in  like  manner.  It  is  evident  that  the 
mixture  attaining  the  smallest  volume  possesses  greatest  density. 

It  must  not  be  forgotten  that  all  of  these  tests  are  equally 
applicable  to  fine  and  coarse  ingredients,  and  the  operator  is 
compelled  to  rely  on  his  own  judgment  as  to  what  shall  be  the 
maximum  size  used  in  his  aggregate.  This  is  a  matter  of  great 


PROPORTIONING.  23 

importance,  as  tests  show  conclusively  that  strength  is  greatly 
augmented  by  admixture  of  coarse  gravel  or  broken  stone,  while 
it  is  not  hard  to  see  the  rapid  increase  in  density  and  the  marked 
saving  in  cement  which  result  from  the  introduction  into  a  fine 
mixture  of  a  considerable  amount  of  coarser  aggregate. 

The  customary  manner  of  specifying  proportions  by  volume 
is  inaccurate  and  misleading.  There  is  a  marked  difference  in 
the  volume  of  a  given  weight  of  cement  packed  and  the  same 
weight  loose.  The  volume  of  sand  increases  with  the  addition 
of  moisture,  owing  to  water  tension  between  the  grains,  and  the 
volume  of  fine  sand  increases  under  such  conditions  more  rapidly 
than  does  coarse.  The  relative  weight  and  volume  of  gravel 
and  broken  stone  vary  greatly,  being  lighter  when  the  particles 
are  of  uniform  size  and  heavier  when  they  are  correctly  graded. 
Proportions  should,  therefore,  be  stated  by  weight  in  all  cases 
where  accuracy  is  desired. 


CHAPTER  VII. 
MIXING. 

THE  incorporation  of  the  various  ingredients  of  concrete 
into  a  homogeneous  mass,  the  manipulation  of  the  mass  until 
its  constituents  are  uniformly  distributed,  and  that  extent  of 
turning  and  stirring  necessary  to  secure  an  even  percentage  of 
moisture  throughout  the  whole,  constitute  essential  factors  of 
success  or  failure  in  concrete-block  manufacture.  Indeed,  in 
all  concrete  work,  mixing  is  a  feature  so  essential  that  its  neglect 
entails  failure,  while  a  recognition  of  its  importance  oftentimes 
averts  the  failure  that  might  be  anticipated  from  negligence  in 
other  branches  of  the  process  of  concreting.  This  importance  is 
accentuated  in  concrete-block  work,  because  the  duty  required 
of  the  blocks,  in  proportion  to  the  bearing  area  of  solid  mate- 
rial therein,  requires  a  uniform  strength  and  density,  which  is, 
in  other  forms  of  concrete  work,  to  a  certain  extent  overcome 
by  the  volume  of  material,  and  the  support  afforded  by  the  adja- 
cent mass  of  material.  Further  than  this,  those  peculiar  quali- 
ties of  impermeability,  uniformity  of  color  and  beauty  of  decora- 
tion, are  demanded  in  block  work  to  a  far  greater  extent  than 
required  in  the  classes  of  construction  to  which  monolithic  work 
is  especially  adapted.  It  is  only  by  most  thorough  manipulation 
that  these  qualities  may  be  developed  in  satisfactory  degree. 
Indeed,  in  relation  to  strength,  and  to  a  certain  extent  in  rela- 
tion to  the  other  qualities  mentioned,  a  careful  attention  to  mixing 

24 


MIXING.  25 

may  serve  to  greatly  overcome  faults  arising  from  ignorance  of 
other  scientific  principles  of  block-making,  or  from  carelessness 
in  the  application  of  those  principles.  While  by  no  means 
encouraging  the  use  of  lean  mixtures,  while  thoroughly  cog- 
nizant of  the  importance  of  correct  proportioning,  and  while 
advising  the  strictest  adherence  to  other  well-determined  essen- 
tials as  outlined  in  other  chapters,  the  facts  must  be  recognized 
as  established  by  those  tests  which  have  proven  that  a  thoroughly 
mixed  lean  concrete,  and  even  a  thoroughly  mixed  ill-propor- 
tioned concrete,  affords  results  more  satisfactory  than  a  rich 
and  well-proportioned  concrete  of  indifferent  mixing.  The  rea- 
son is  easily  found.  It  has  already  been  said  that  the  theory 
of  concrete  involves  the  thorough  coating  of  every  fine  particle 
of  the  aggregate  with  cement-paste,  and  the  coating  of  every 
coarse  particle  of  the  aggregate  with  sand  and  cement  mortar. 
It  is  evident  that  this  can  be  accomplished  in  no  other  way  than 
by  most  thorough  mixing.  It  has  also  been  said  that  the  theory 
of  proportioning  involves  such  gradation  of  aggregate  that  the 
finer  particles  will  tend  to  fill  the  voids  of  the  succeeding  larger 
sizes.  It  is  evident  that  nothing  but  mixing  can  attain  this 
desirable  result,  as  faulty  mixing  will  leave  the  various  sizes  of 
aggregate,  as  well  as  the  aggregate  and  the  cement,  each  gathered 
to  itself,  instead  of  becoming  distributed  evenly  throughout  the 
whole. 

The  order  of  incorporating  ingredients  has  been  considered 
a  matter  of  so  great  importance  that  it  is  particularly  mentioned 
in  all  standard  concrete  specifications,  although  the  practice  of 
most  cement-block  makers  is  to  disregard  any  particular  order 
and  dump  cement,  sand,  gravel,  and  water  together  indiscrimi- 
nately. In  hand-mixing  under  railroad,  municipal,  or  govern- 
ment specifications,  predetermined  quantities  of  the  various 
sizes  of  aggregate  ar.e  measured  in  boxes  having  no  bottom  or 


20  CONCRETE-BLOCK  MANUFACTURE. 

top,  so  that  when  the  box  is  filled  it  may  be  lifted  from  the  mea- 
sured material.  The  sack  is  the  unit  of  cement  measurement. 
The  required  amount  of  sand  is  first  spread  on  the  mixing-plat- 
form, which  should  be  water-tight  and,  if  possible,  non-absorbent. 
The  cement  is  then  spread  to  an  even  thickness  on  the  sand,  and 
the  two,  by  means  of  hoes  or  square-pointed  shovels,  are  turned 
together  two  or  three  times,  or  until  of  an  even  color,  when  the 
water  is  either  sprayed  on  the  mixture  from  a  hose-nozzle  or 
poured  (but  not  dashed)  into  the  center  of  the  material  pre- 
viously thrown  into  the  form  of  a  ring  or  crater.  The  latter 
method  is  considered  better  practice,  as  affording  accurate  mea- 
surement of  water.  The  mixture  is  then  turned  twice,  the  per- 
centage of  water  being  such  as  to  form  a  rather  wet  mortar. 
The  gravel  or  broken  stone,  previously  wet  to  avoid  further 
absorption,  is  then  spread  on  the  mortar  and  the  turning  con- 
tinued until  uniform  throughout  the  whole.  It  is  evident  that 
such  careful  methods  secure  the  maximum  quality  possible  for 
hand-mixing.  It  has,  however,  been  the  practice  of  block-makers 
to  mix  all  materials  dry  and  afterward  apply  the  water,  the  latter 
usually  being  unmeasured,  and  then  mix  until  approximate  uni- 
formity results.  While  the  evils  of  this  method  are  partially 
obviated  by  dry-mixing  to  secure  uniform  color  before  wetting, 
it  is  obvious  that  the  degree  of  homogeneity  possible  by  obser- 
vance of  standard  specifications  cannot  obtain;  and  it  is  to  this 
cause  that  weakness,  porosity,  permeability,  and  lack  of  uni- 
formity in  color  are  often  traceable. 

Hand-mixing  is  at  best  a  method  which  should  be  employed 
only  until  the  business  of  the  plant  warrants  the  installation  of 
a  good  power-mixer,  or  upon  special  work  in  isolated  localities 
which  may  not  justify  the  full  plant  equipment.  There  are 
several  reasons  which  should  induce  one,  in  equipping  a  plant, 
to  include  a  power-mixer.  The  reduction  in  labor  is  a  cost  item 


MIXING.  27 

of  great  consequence,  as  one  reason  for  defective  hand- mixing 
is  the  large  expense  for  labor  necessary  to  secure  really  good 
results.  The  work  done  by  power-mixing  is  not  only  vastly 
superior  to  hand- work  in  quality,  but,  if  batches  be  run  for  equal 
periods  of  time,  possesses  the  virtue  of  absolute  uniformity. 
Actual  tests  upon  hand-  and  machine-mixing  show  a  gain  in 
strength  for  the  latter  which  fully  justifies  the  initial  outlay. 

There  are  so  many  different  kinds  of  mixers  on  the  market 
to-day  that  the  block-maker  may  err  greatly  in  selection.  The 
cheapest  may  prove  most  expensive  on  account  of  inefficiency, 
There  are  two  classes  of  mixers  which  cannot  be  recommended 
for  block  work.  The  mixers  operated  by  hand  are  but  poor 
makeshifts,  which  scarcely  give  as  good  results  for  the  same 
amount  of  labor  as  do  square-pointed  shovels.  Of  the  power- 
mixers,  the  continuous  type  is  not  well  adapted  to  block  work, 
for  two  reasons.  In  the  first  place,  too  much  depends  upon 
the  order  in  which  the  materials  are  introduced  into  continuous 
mixers,  and  therefore  the  materials  must  be  spread  in  layers, 
in  much  the  same  manner  as  described  in  the  preliminary  oper- 
ations of  hand-mixing;  and  shovelfuls  of  material  for  deposit 
in  the  mixer  must  cut  perpendicularly  through  the  several  layers, 
so  that  the  shovel  will  contain  the  same  relative  proportions  as 
desired  in  the  mixed  material.  In  the  second  place,  the  time 
of  mixing  is  mechanically  determined,  and  the  manipulation 
cannot  be  increased  even  though  the  advantages  of  longer  mixing 
may  be  clearly  apparent. 

The  batch -mixers,  operated  by  steam,  gasoline  engine,  or 
electric  motor,  are  especially  adapted  to  concrete-block  work, 
because  the  mixing  may  be  continued  at  will,  and  thus  any  desired 
degree  of  uniformity  is  dependent  only  upon  the  time  that  the 
batch  is  run.  Consequent  upon  this  advantage  is  that  other 
important  consideration  that  the  order  in  which  the  material  is 


28  CONCRETE-BLOCK  MANUFACTURE. 

discharged  is  entirely  independent  of  the  order  in  which  it  enters 
the  mixer.     Batch-mixers  mix  thoroughly,  while  the  more  com- 


FiG.   i. — Rotary  Mixer. 


FIG.  2. — Cube  Mixer. 


mon  forms  of  continuous  mixers  are  modified  conveyors,  cal- 
culated to  effect  greater  or  less  stirring  of  the  material  as  it  is 


MIXING. 


29 


conveyed  from  entry  to  discharge.  Fig.  i  shows  a  rotary  mixer 
in  which  deflecting  blades  throw  the  material  from  end  to  end 
as  the  mixer  revolves.  Fig.  2  shows  a  revolving  cube-mixer 


in  which  the  shape  of  the  mixing-box  is  relied  upon  to  accom- 
plish the  same  result  without  interior  deflectors.  Both  of  the 
types  shown  have  given  excellent  satisfaction  in  actual  use. 


30  CONCRETE-BLOCK  MANUFACTURE. 

While,  in  using  a  mixer  of  a  type  similar  to  those  illustrated, 
all  materials  for  a  batch  may  be  put  in  at  one  time  and  no  atten- 
tion given  to  the  order  in  which  they  are  introduced,  yet  much 
better  results  will  be  obtained  by  running  the  batch  dry  until 
it  is  well  mixed  before  introducing  water  into  the  mixer,  and 
afterward  running  the  batch  wet  as  long  as  may  be  necessary. 

Whether  mixing  be  by  hand  or  machine,  it  is  essential  that 
the  initial  set  of  the  cement  be  avoided  by  so  regulating  the  size 
of  batch  in  proportion  to  the  capacity  of  the  block-machine  that 
no  cement  will  be  wet  over  thirty  minutes. 


CHAPTER  VIII. 

SHAPE   OF  BLOCKS. 

IN  considering  the  many  shapes  of  blocks  now  used  for  form- 
ng  hollow  walls,  the  question  naturally  asked  is,  "  Why  so  much 
talk  of  hollow  walls,  and  what  are  their  advantages?  "  In  reply 
it  may  be  said  that  the  chief  advantages  of  hollow  walls  over 
solid  walls  are  four  in  number,  viz.:  Insulation  against  heat 
and  cold,  saving  of  material,  water-tightness,  and  ventilation.' 

The  fact  that  a  considerable  air-space  between  the  face  of 
a  wall  exposed  to  the  weather  and  the  interior  face  largely  pre- 
cludes the  passage  of  heat  has  been  too  well  established  to  admit 
of  discussion.  The  result  is,  of  course,  that  the  rooms  of  a  build- 
ing are  more  comfortable  in  summer  on  account  of  the  heat 
of  the  exterior  surface  not  being  transmitted  to  the  interior,  while 
in  winter  the  conditions  are  reversed  and  the  interior  surface  does 
not  lose  its  artificial  heat  through  transmission  to  the  exterior. 
It  is  a  fact  that  approximately  25%  of  heating-bills  may  be 
saved  by  properly  constructed  hollow  concrete  walls.  A  man  who 
purchased  a  concrete- block  house  during  the  past  summer,  but 
who  was  not  informed  as  to  the  real  merits  of  this  material, 
recently  remarked:  "The  furnace  in  that  house  is  a  remark- 
ably good  one;  it  is  surprising  how  small  a  fire  makes  the  rooms 
comfortable."  Doubtless  it  was  a  good  furnace,  but  the  reason 
of  the  noticeable  warmth  from  a  small  fire  was,  that  the  heat 

31 


32  CONCRETE-BLOCK  MANUFACTURE, 

remained  in  the  house  instead  of  passing  through  a  solid  wall 
and  disseminating  itself  throughout  the  surrounding  country. 


FIG.  4.— Three-web  Hollow  Blocks  and  Wall.    ^^^ 

The  saving  in  material  is  an  important  item  to  the  block- 
maker  and  to  his  customer.      In  the  hole  in  the  wall  lies  the 


SHAPE   OF  BLOCKS.  33 

maker's  profit  and  the  consumer's  saving.  Originally  blocks 
were  designed  with  from  20%  to  33%  air-space,  but  modern 
methods  of  proportioning,  compacting,  curing,  and  bonding 
have  so  greatly  increased  the  efficiency  of  concrete  blocks  in 
relation  to  the  actual  amount  of  solid  material  that  walls  are 
frequently  laid  with  from  50%  to  55%  of  air-space,  and  still  pre- 
serve a  factor  of  safety  which  insures  conservative  construction. 

The  fact  that  concrete  is  not  absolutely  waterproof,  and  as 
commonly  made  is  not  approximately  so,  was  doubtless  one  of 
the  principal  reasons  for  the  original  introduction  of  an  air-space 
in  the  wall,  the  separation  of  the  outer  and  inner  face  being 
designed  to  prevent  water  penetrating  beyond  the  intermediate 
air-chamber. 

Ventilation  in  the  sense  here  intended  is  a  consideration 
usually  overlooked.  It  is,  of  course,  well  known  that,  by  the 
use  of  ventilators  similar  to  the  usual  hot-air  register,  any  desired 
circulation  of  air  may  be  established  between  the  outer  atmos- 
phere and  the  air  of  a  room  through  the  vertical  air-chambers 
in  the  hollow  wall.  This  is,  however,  not  the  thought  now  in 
mind,  but  rather  the  gradual,  unrecognizable,  but  nevertheless 
constant,  absorption,  through  the  pores  in  the  concrete,  of  the 
dampness  and  injurious  gases  accumulating  in  every  occupied 
room.  It  is  the  suction  of  the  gases  and  vapor  by  the  air  in  the 
wall  that  gives  to  block  construction  its  great  sanitary  virtue, 
and  hence  the  elimination  of  sweating  on  the  interior  is  a  notice- 
able feature  of  block  construction. 

In  Fig.  3  is  shown  one  of  the  earliest  forms  of  hollow  blocks 
introduced  in  the  United  States,  a  form  which  has  been  used  in 
a  very  large  number  of  buildings,  a  form  which  has  been,  with 
slight  changes,  adopted  by  very  many  manufacturers  of  machines, 
and  a  form  which  in  its  essential  features  stands  for  the  hollow- 
block  construction  of  to-day.  It  will  be  noted  that  the  form  is 


34  CONCRETE-BLOCK  MANUFACTURE. 

very  simple,  having  a  transverse  web  at  either  end  and  two 
transverse  webs  midway  of  the  block,  so  that  a  half  block,  which 
is  an  essential  feature  in  all  block  construction,  is  made  without 
change  of  cores.  Special  attention  is  called  to  the  L-shape  cor- 
ner-block used  in  connection  with  this  form,  as  some  of  the  later 
types  of  hollow  blocks  eliminate  this  feature  and  merely  use 
regular  blocks  extending  through  at  corners,  with  the  end  web 
flush  with  the  front  and  back  of  the  block  to  form  a  corner  return. 

The  block  illustrated  in  Fig.  4  is  not  essentially  different 
from  that  shown  in  Fig.  3,  the  only  material  variance  being  in 
the  use  of  one  intermediate  web  instead  of  two.  Measured  by 
the  number  of  machines  producing  it,  this  is  by  far  the  most 
common  type  of  block.  There  are  at  least  twenty  moulds  and 
machines  now  advertised  in  trade-journals  for  making  blocks 
with  the  three  cross-sections  by  using  two  interior  cores,  and 
the  type  is  common  to  upright  and  face-down  machines. 

The  single  air-space  block,  involving  the  elimination  of  the 
middle  web  and  the  use  of  but  one  interior  core,  is  a  later  develop- 
ment, and  hence  less  common  than  the  form  last  mentioned. 
This  block  possesses  some  advantage,  inasmuch  as  any  reduc- 
tion in  the  number  and  size  of  cross-partitions  reduces  the  lia- 
bility to  penetration  of  moisture  in  case  of  heavy  rains.  It  is 
also  more  easy  to  tamp  around  one  core  than  to  tamp  around 
and  between  two  or  more,  and  hence,  with  the  average  grade 
of  labor  employed,  a  more  thoroughly  and  uniformly  compacted 
block  will  result.  The  releasing  is  also  facilitated,  and  the  danger 
of  tearing  blocks  in  removing  cores  is  somewhat  lessened,  while 
there  is  a  slight  saving  in  material.  This  is  a  very  simple  form 
for  those  who  prefer  to  make  their  own  molds  of  wood  instead 
of  purchasing  any  of  the  standard  machines.  The  author  recently 
inspected,  in  the  State  of  Washington,  a  $5 ,000  residence,  nearing 
completion,  in  which  all  walls  above  ground-line  were  of  this 


SHAPE   OF  BLOCKS. 


35 


type  of  block,  made  in  wooden  molds  locally  manufactured.  The 
work  was  most  creditable,  but,  in  justice  to  those  who  may  desire 
to  go  and  do  likewise,  it  should  be  said  that  the  company  building 
the  house  mentioned  had  in  its  employ  a  most  expert  model- 
maker  and  a  cement-worker  of  equal  ability. 

Fig.  5  represents  an  attempt  to  combine   the  one-piece  and 
the  two-piece  form  by  the  use  of  slabs  united  by  metal  rods  or 


FIG.  5. — Blocks  consisting  of  Two  Slabs  connected  by  Metal  Ties. 

• 

ties,  the  ends  of  which  are  imbedded  in  the  outer  and  inner 
slabs.  The  object  is  to  secure  a  continuous  air-space  of  uniform 
size  throughout  the  wall.  This  form  of  block  has  been  seri- 
ously criticised  from  an  engineering  standpoint,  and  it  has  been 
stated  that  the  object  sought  is  attained  at  the  expense  of  cor- 
rect construction.  By  its  advocates  the  fact  is  cited  that  metal 
rods  are  extensively  and  satisfactorily  employed  in  reinforced 


36  CONCRETE-BLOCK  MANUFACTURE. 

concrete  work;  while  its  opponents  answer  that,  in  reinforced 
concrete,  the  iron  or  steel  is  protected  from  rust  and  corrosion 
by  the  concrete  in  which  it  is  imbedded,  while,  in  the  type  of 
blocks  illustrated,  the  tie-rods  are  without  such  protection,  and 
therefore  subject  to  deterioration  from  atmospheric  action,  as 
well  as  to  rust  from  the  moisture  penetrating  the  outer  shell  of 
the  wall.  However  this  may  be,  the  fact  remains  that  at  least 
one  house  was  built  ove'r  twenty  years  ago  from  concrete  slabs 
tied  by  metal  rods,  and  is  in  a  good  state  of  preservation  at  the 
present  day.  While  the  form  and  method  of  fastening  the  rods 
vary  slightly  from  that  illustrated  in  Fig.  5,  substantially  the 
same  principles  are  embodied  in  the  blocks  used  in  the  house, 
which  has  two  decades  to  its  credit.  It  may  be  merely  a  coin- 
cidence, or  it  may  be  a  fact  worthy  of  note,  that  this  house  has 
been  repeatedly  struck  by  lightning.  By  some  it  is  claimed 
that  this  is  due  to  the  attraction  of  the  metal  rods.  It  is,  how- 
ever, of  greater  importance  to  observe  that  the  resultant  damage 
has  in  each  case  been  so  slight  that  repairs  were  easily  and  quickly 
made. 

In  Fig.  6  are  shown  blocks  of  the  standard  two-piece  type, 
while  Fig.  7  illustrates  more  plainly  the  method  of  laying  in  the 
wall,  the  continuous  horizontal  air-space,  and  the  method  of 
bonding.  Two-piece  walls  were  brought  out  some  four  years 
ago  with  a  view  of  overcoming  some  of  the  difficulties  of  manu- 
facture attendant  upon  the  making  of  the  one-piece  blocks,  of 
enabling  the  operator  to  follow  more  closely  the  recognized 
standards  of  good  concreting,  of  enabling  the  builder  to  adhere 
to  the  principles  of  the  best  engineering  practice  in  wall-con- 
struction, and  of  affording  a  more  thorough  insulation  than  that 
secured  by  one-piece  blocks.  Care  was  also  taken  to  avoid  all 
of  the  objectionable  features  attendant  upon  efforts  to  construct 
two  walls  with  an  intervening  air-space,  and  this  could  only  be 


SHAPE  OF  BLOCKS. 


37 


accomplished  by  blocks  of  such  shape  that  those  forming  the 
outer  face  should  bond  with   those  forming   the  inner  surface 


FIG.  6.— Two-piece  Blocks  and  Wall. 

by  the  overlapping  of  projections  in  alternate  courses.  The 
immediate  and  continued  success  of  the  two-piece  system,  and 
its  adoption  in  many  structures  of  such  size  and  importance 


FIG.  7. — Diagram  of  Two-piece  Wall,  showing  Air-space  and  Bond. 

that  it  was  scarcely  hoped  that  concrete  blocks  would  be  adopted, 
proves  that  the  best  architects  and  engineers  were  quick  to  recog- 


38  CONCRETE-BLOCK  MANUFACTURE. 

nize  its  points  of  superiority.  The  type  of  block  shown  in  Fig.  6 
is  probably  the  earliest  form  of  two-piece  block  to  come  into 
extensive  commercial  use,  as  the  building  shown  in  Fig.  8  is  the 
earliest  structure  worthy  of  mention  in  which  two-piece  walls 
were  used.  It  is  a  noticeable  fact  that,  though  the  earliest,  this 
type  still  maintains  its  supremacy,  and  is  to-day  regarded  as  the 


FIG.  8.— Angelus  Hotel,  El  Paso,  Texas. 

acme  of  perfection,  because  the  lines  of  the  block  are  correct 
from  the  engineer's  and  the  architect's  point  of  view.  It  will  be 
noted  that,  while  a  modification  of  the  T-shape,  it  possesses  a 
distinct  advantage  in  the  short  reinforcing  arms  at  either  end 
of  the  face-section.  It  has  strength  in  its  various  parts  in  pro- 
portion to  stresses  which  it  is  called  upon  to  withstand,  and  not 
only  breaks  joints  between  courses,  but  breaks  joints  laterally 


SHAPE   OF  BLOCKS.  39 

in  every  course,  thus  leaving  no  vertical  joints  extending  through 
the  wall,  and  giving  the  same  result  as  established  methods  of 
bonding  in  brick  and  stone  work  by  the  alternate  overlapping 
of  long  and  short  arms.  It  is  in  the  manufacture  of  this  block 
that  one  of  its  great  advantages  lies.  As  each  block  has  but 
one  face,  interior  cores  are  eliminated,  and  it  becomes  possible 
to  make  the  blocks  under  direct  and  instantaneous  pressure  with- 
out the  use  of  a  tamper.  This  practice  permits  the  use  of  as 
large  a  percentage  of  water  as  may  be  necessary  to  fulfill  the 
requirements  of  standard  engineering  specifications  for  a  medium 
or  quaking  mixture,  and  at  the  same  time  it  allows  the  use  of 
as  large  size  aggregate  as  may  be  desired.  Thus  not  only  is  a 
much  more  thorough  crystallization  secured  in  the  initial  set 
than  is  possible  with  a  dry  mixture,  but  far  greater  strength 
and  density  are  obtained  than  can  be  possible  in  a  sand  and 
, cement  mixture.  One  of  the  most  notable  advantages  of  this 
block  lies  in  the  facility  with  which  a  continuous  horizontal  air- 
space is  produced  throughout  the  wall,  as  shown  in  Fig.  7,  by 
leaving  open  the  interior  vertical  joints.  This  is  entirely  prac- 
ticable without  loss  of  strength,  owing  to  the  indestructible  bond 
in  the  wall.  This  horizontal  air-space  is  valuable  in  relation 
to  every  phase  of  insulation,  but  particularly  because  of  its  pre- 
vention of  the  penetration  of  moisture  by  capillary  attraction 
and  the  consequent  insurance  of  a  dry  interior  in  damp  weather. 
Fig.  9  shows  the  adaptability  of  two-piece  blocks  to  mul- 
tiple air-space  construction  by  so  arranging  the  blocks  that  an 
interlocking  bond  is  secured.  The  extension  of  the  same  prin- 
ciple to  include  a  number  of  members  greater  than  three  may 
be  utilized  to  build  a  wall  of  any  desired  thickness.  Such  walls 
are  very  serviceable  for  any  heavy  construction,  and  are  especially 
designed  to  meet  the  requirements  of  cold-storage  plants,  ice- 
houses, or  any  buildings  requiring  unusual  insulation. 


40  CONCRETE-BLOCK  MANUFACTURE. 

Fig.  10  shows  a  one-piece  block  of  a  pattern  radically  different 
from  those  heretofore  described.  The  idea  of  this  block  is  to  so 
dispose  the  webs  and  hollow  spaces  that  each  web  will  be  backed 
by  an  air-chamber,  and  that  no  portion  of  the  solid  concrete 
will  extend  directly  from  the  outer  face  of  the  wall  to  the  inner 
side,  the  object  sought  being  resistance  to  penetration  of  mois- 


FIG.  9. — Interlocking  Three-member  Wall. 

ture  by  rendering  it  impossible  for  capillary  attraction  to  draw 
water  to  the  interior  of  a  building  except  by  a  route  so  circuitous 
as  to  be  an  impossible  pathway.  These  blocks  have,  during  the 
past  two  years,  been  extensively  introduced,  especially  through- 
out the  Mississippi  Valley,  where  the  humidity  is  great  and  the 
demand  for  dry  walls  imperative.  They  have  accomplished  the 
purpose  for  which  they  are  designed  in  an  admirable  manner, 


SHAPE  OF  BLOCKS.  41 

and,  in  every  case  where  due  attention  was  given  to  proportion- 
ing mixing  and  compacting,  have  given  general  satisfaction.  A 
press  was  formerly  employed  in  ,  manufacturing  blocks  of  this 
type;  but  as  they  must  be  made  in  an  upright  position,  the  form 
prohibiting  their  manufacture  in  either  a  face-up  or  a  face-down 
machine,  the  press  was  discarded,  and  they  are  now  generally 
made  by  tamping  in  molds  of  the  "  roll-over  "  style. 

It  is  not  claimed  for  this  chapter  that  it  describes  in  detail 
all  of  the  points  involved  in  any  particular  shape  of  block.  It 
is  manifestly  aside  from  the  scope  of  this  work  to  give  the  minute 


FIG.  10. — Block  with  Staggered  Air-space. 

details  of  the  many  variations  in  the  shape  of  nearly  all  of  the 
types  mentioned.  It  has  rather  been  the  purpose  to  present 
some  of  the  more  patent  advantages  and  disadvantages  of  the 
general  types  illustrated,  which  may  be  said  to  fairly  cover  the 
more  decidedly  novel  features  of  the  many  styles  of  blocks  on 
the  market. 

To  one  who  follows  the  subject  closely,  the  thought  cannot 
fail  to  come  that  too  much  inventive  genius  is  devoted  to  devising 
various  shapes  of  concrete  blocks.  From  week  to  week,  and 
from  month  to  month,  the  designs  of  different-shaped  blocks 
have  increased  in  number  until  they  are  as  the  sands  of  the  sea- 


42  CONCRETE-BLOCK  MANUFACTURE. 

shore, — no  man  can  number  them.  If  any  good  could  possibly 
come  to  mankind  from  this  waste  of  genius,  it  would  be  very 
far  from  the  purpose  of  this  work  to  criticise  those  who  are  devoting 
their  time  to  the  fruitless  task.  There  is,  however,  in  this  mul- 
tiplicity of  designs  no  added  usefulness  developed,  no  novel 
features  displayed,  and  no  step  taken  which  will  aid  the  advance- 
ment of  the  industry.  The  sole  idea  of  the  present-day  block- 
designers  appears  to  be  the  avoidance,  by  the  slightest  change 
possible,  of  the  rights  of  those  who  have  preceded  them.  If  the 
childish  variations  which  are  made  were  meritorious,  it  would 
be  well.  In  general,  it  does  the  changers  no  injustice  to  say 
that  their  alterations  are  detrimental.  Indeed,  very  many  of 
them  are  never  intended  for  commercial  use,  while  others  are  so 
impracticable  that  any  effort  to  use  them  in  actual  practice  can 
only  result  in  absolute  failure.  What  the  concrete-block  indus- 
try needs  is  better  workmen  rather  than  more  geniuses. 


CHAPTER  IX. 

PROCESSES. 

IN  considering  the  processes  of  concrete- block  manufacture, 
it  is  necessary  to  consider  only  the  methods  used  in  compacting 
the  mass,  because  the  operations  before  and  after  this  part  of 
the  process  are,  except  as  to  the  amount  of  water  used  and  the 
size  of  aggregate,  identical.  It  is,  however,  desirable  to  note 
that,  while  the  subject-matter  of  this  chapter  has  been  the  cause 
of  unlimited  contention,  it  is  not  more  essential  to  successful 
work  than  the  preliminary  proportioning  and  mixing,  or  the 
final  curing.  While  the  nature  of  general  concrete  work  and 
the  necessities  in  connection  with  depositing  the  concrete  in 
place  admitted  of  but  two  methods  of  compacting  the  mass, 
namely,  ramming  or  pouring,  the  altered  conditions  in  a  con- 
crete-block factory  have  introduced  the  additional  factor  of 
pressing,  and  each  of  these  three  methods  has  again  been  divided, 
so  that  we  have  six  different  processes: 

1.  Hand-tamping. 

2.  Pneumatic  tamping. 

3.  Pouring  in  iron  molds. 

4.  Casting  in  sand. 

5.  Mechanical  pressure,  both  hand  and  power. 

6.  Hydraulic  pressure. 

43 


44 


CONCRETE-BLOCK  MANUFACTURE. 


In  hand-tamping  the  best  possible  results  are  obtained  by 
light  and  frequent  ramming  of  a  dry  mixture  of  sand  or  screenings 
and  cement.  The  use  of  a  dry  mixture  is  necessary  to  cause  the 
mass  to  compact  under  the  blows  of  the  tamper  instead  of  squash- 
ing, or  being  thrown  outside  the  area  of  contact,  by  the  force  of 
the  blow.  It  is  only  in  a  dry  mixture  that  the  quick  adhesion 
of  particles  obtains,  which  is  necessary  to  prevent  dislodgment 
of  those  portions  already  tamped  by  blows  upon  adjacent  por- 


FIG.  ii. — Pneumatic  Tamper  in  Operation. 

tions  of  the  mass.  For  similar  reasons,  the  use  of  a  coarse  aggre- 
gate is  impracticable. 

Successful  block-making  by  hand-tamping  is  a  matter  of 
industry  and  endurance.  To  reduce  the  labor  and  secure  uni- 
formity in  the  product,  pneumatic  tampers  similar  to  that  shown 
in  operation  in  Fig.  n  are  now  used  in  a  considerable  number 
of  factories  with  good  results.  Their  action  is,  of  course,  rapid 
and  uniform,  and  the  work  much  lighter. 

The  process  of  pouring  in  iron  moulds  was  designed  to  secure 
greater  strength  by  using  a  large  percentage  of  water  to  over- 


PROCESSES.  45 

come  the  lack  of  crystallization  in  the  initial  set  of  a  dry  mix- 
ture. As  the  mass  is  reduced  to  a  fluid  state,  it  settles  to  place 
in  the  molds  by  its  own  weight  and  results  in  a  very  hard  block 
To  this  process  there  are  three  valid  objections.  The  top  and 
bottom  of  a  block,  considered  according  to  its  position  in  the 
mold,  are  not  uniform,  as  the  heavier  particles  gravitate  toward 
the  bottom.  Owing  to  the  time  required  for  a  very  wet  mix- 
ture to  absorb,  or  throw  off,  enough  of  the  water  that  the  block 
may  attain  sufficient  rigidity  to  prevent  deformation  when  the 
support  is  removed  from  its  side,  the  mold  is  in  service  several 
hours  for  each  block  manufactured,  and  therefore  a  very  large 
number  of  molds  must  be  provided  to  produce  the  output  of  a 
moderate-size  factory.  No  satisfactory  surface  for  fine  work 
can  be  obtained  by  the  simple  act  of  pouring  concrete  into  an 
iron  mold,  and  it  becomes  necessary  to  produce  a  face  by  aux- 
iliary treatment.  This  is  accomplished  in  various  ways.  By 
one  method  the  mold  is  arranged  so  that  the  face  of  the  block 
will  be  uppermost  and  it  is  smoothed,  and,  while  ver-y  wet,  coated 
with  screened  marble-dust,  giving  a  fine  granular  texture  to  the 
surface.  By  another  method  the  blocks  are  chipped  by  hand 
while  in  a  semi-plastic  state,  and  thus  an  imitation  of  pitch-face 
stone-work  is  secured. 

Casting  in  sand  is  not  in  very  general  use  for  ordinary  block- 
making  in  this  country,  owing  to  the  expense  incident  to  this 
method  of  manufacturing.  It  has,  however,  been  extensively 
used  for  the  making  of  blocks  for  all  portions  of  buildings  in 
Havana,  Cuba,  and  is  largely  used  in  the  making  of  ornamental 
work  in  the  United  States.  The  process  is  on  the  same  general 
lines  of  casting  as  followed  by  iron-molders,  and  results  in  blocks 
that  are  not  only  very  hard  and  very  durable,  but  that  accurately 
follow  the  detail  of  the  pattern  and  present  a  beautifully  finished 
appearance. 


46  CONCRETE-BLOCK  MANUFACTURE. 

The  possibilities  attendant  upon  the  condensation  of  con- 
crete blocks  by  mechanical  pressure  are  of  recent  discovery. 
It  is  within  the  last  three  years  that  both  hand-  and  power-presses 
have  been  devised  for  successfully  producing  high-grade  blocks 
with  a  saving  of  labor  which  has  brought  the  manufacturing  cost 
below  that  of  older  processes.  The  principle  upon  which  this 
development  is  based  is  that,  by  confining  in  a  mold,  properly 
vented  for  escape  of  air,  a  medium-wet  mixture  of  coarse  con- 
crete, of  which  the  larger-size  aggregate  may  measure  from  f" 
to  i"  in  its  greatest  diameter,  and  simultaneously  applying  to 
every  part  of  the  exposed  area  of  the  concrete  an  instantaneous 
pressure  by  power  sufficient  to  thoroughly  condense  the  mass, 
a  more  dense  and  homogeneous  block  can  be  secured  than  by 
any  formerly  mentioned  process.  The  fact  that  blocks  so  made 
have  withstood  the  most  severe  tensile,  compressive,  and  fire 
tests  proves  the  correctness  of  this  theory.  The  fact  that  blocks 
so  pressed  have  been  used  in  several  of  the  most  important  struc- 
tures yet  built  of  blocks  is  sufficient  recommendation  of  its  suc- 
cess from  a  practical  view-point.  In  pressing  blocks  it  is  essen- 
tial that  voids  be  eliminated  by  adequate  provision  of  means 
by  which  the  air  contained  in  the  mass  of  loose  concrete  may 
escape.  It  is  also  essential  that  means  be  provided  for  deter- 
mining that  each  block  is  uniformly  pressed.  This  may  be 
done  either  by  suitable  device  for  measuring  pressure,  or  by 
adjusting  the  press  to  an  arbitrary  stop.  In  the  latter  case  the 
concrete  must  be  uniformly  mixed,  uniformly  deposited,  and 
the  mold  filled  to  a  uniform  height. 

The  application  of  hydraulic  pressure  to  block-making  is  not 
of  so  recent  origin  as  the  application  of  mechanical  pressure; 
but  the  former  has  not  met  with  universal  introduction,  because, 
while  the  degree  of  compactness  secured  has  ever  commanded 
recognition,  the  time  required  in  the  manipulation  of  a  hydraulic 


PROCESSES.  47 

press  has  been  an  obstacle  easily  overcome  by  use  of  mechanical 
pressure.  Recently,  however,  large  presses  have  been  con- 
structed in  which  a  number  of  blocks  may  be  pressed  at  one  time ; 
and,  though  cumbrous,  this  later  development  offsets  to  a  degree 
the  objectionable  feature  of  the  'time  lost  in  making  a  single 
hydraulic  pressure. 


CHAPTER  X. 

PLASTICITY. 

THE  question  of  normal  consistency  of  concrete  for  block- 
manufacture  has  been  too  largely  determined  by  prejudice 
instigated  by  manufacturers  whose  machines  were  adapted  to 
but  a  single  degree  of  plasticity.  This  is  to  be  deplored,  inas- 
much as  the  value  of  those  well-defined  principles  underlying 
good  concrete  construction  is  greater  than  the  value  of  any  par- 
ticular machine,  or  any  particular  type  of  machines.  These 
principles  have  gradually  been  deduced  from  results  obtained 
from  actual  work  under  varying  conditions  during  that  period 
of  years  since  cement  assumed  its  place  as  an  important  factor 
in  the  industrial  life  of  the  nineteenth  century.  The  best  engineer- 
ing talent  of  the  great  railways,  and  of  our  national  government, 
has  been  directed  toward  the  ascertainment  of  those  practices 
which  would  result  in  concrete  work  of  the  greatest  strength 
and  durability;  and  for  the  almost  unanimous  decision  reached, 
that  a  medium-wet  mixture  should  be  used  whenever  practicable, 
there  must  be  a  reason.  It  is  to  be  found,  in  the  first  place,  in 
the  chemical  action  produced  in  the  cement  by  the  addition  of  a 
proper  proportion  of  water.  In  common  parlance,  this  chemical 
activity  is  described  as  setting,  or  crystallization.  The  exhaustive 
researches  of  Le  Chatelier  have  not  only  established  the  fact 
that  tricalcium  silicate  is  the  essential  chemical  element  in  the 
setting  of  Portland  cement,  but  that  crystallization  only  ensues 

48 


PLASTICITY.  49 

after  sufficient  water  has  been  consumed  to  decompose  this  tri- 
calcium  silicate.  In  the  second  place,  aside  from  any  chemical 
question,  the  mere  mechanical  problem  of  coating  the  aggregate 
and  filling  the  voids  is  sufficient  ground  for  abandoning  the  use 
of  an  ultra-dry  mixture. 

What  is  ordinarily  known  as  a  dry  mixture  is  of  the  con- 
sistency of  damp  earth.  If  a  lump  of  dry  concrete  be  com- 
pressed in  the  hand,  it  will  not  give  off  sufficient  water  to  soil 
the  hand,  but  it  will  instantly  acquire  sufficient  rigidity  to  retain 
its  shape.  It  is  this  latter  quality  which  has  brought  dry  con- 
crete into  such  favor  in  connection  with  block  work.  The  fact 
that  it  would  instantly  hold  the  position  to  which  it  was  rammed 
by  the  tamper,  and  that  the  face-plates  could  forthwith  be  with- 
drawn from  the  block,  has  been  so  great  a  factor  in  facilitating 
the  manufacture,  and  consequently  in  reducing  the  cost,  of  the 
product  that  those  well-established  scientific  principles  which 
make  for  quality  have  been  sacrificed  to  speed  and  cheapness. 
In  all  frankness  it  must  be  said  that  the  dire  effects  of  the  use 
of  a  mixture  so  dry  as  to  cause  weak  blocks,  liable  to  disintegration 
within  a  few  years,  is  not  wholly  chargeable  to  the  manufacturers 
of  machines.  They  customarily  recommend  the  use  of  a  mix- 
ture as  wet  as  practicable;  but  this  passes  the  matter  on  to  oper- 
ators of  whom  too  many,  ignorant  of  the  principles  underlying 
the  business  in  which  they  have  engaged,  interpret  this  instruc- 
tion as  a  license  for  them  to  use  the  mixture  which  they  can 
manipulate  with  the  greatest  ease. 

It  is,  however,  only  in  machines  which  make  blocks  by  tamp- 
ing that  the  ultra-dry  mixture  is  available.  The  medium  mix- 
ture is  used  in  all  machines  operated  by  pressure,  whether  hand, 
mechanical  power,  or  hydraulic.  By  a  medium  mixture  is  meant 
one  containing  so  much  moisture  that  it  will  quake,  and  water 
will  flush  to  the  surface  when  the  mass  is  compressed.  It  is  not 


50  CONCRETE-BLOCK  MANUFACTURE. 

possible  to  specify  an  unvarying  percentage  of  water  without 
acquaintance  with  local  materials.  In  general,  it  may  be  said 
that  a  broken-stone  aggregate  will  require  a  larger  percentage 
of  water  than  would  be  needed  in  concrete  made  from  sand  and 
gravel  aggregate.  By  the  use  of  a  medium-wet  mixture  a  more 
thorough  crystallization  is  secured  in  the  initial  set  of  the  cement, 
and  a  better  concrete  is  obtained  by  reason  of  more  thorough 
coating  of  the  aggregate  and  more  complete  filling  of  voids. 

A  wet  mixture  is  used  only  in  poured  work,  and  involves 
the  use  of  so  much  water  as  to  reduce  the  concrete  to  a  fluid 
mixture  suitable  for  pouring,  and  requiring  neither  tamping 
nor  pressure.  From  a  chemical  point  of  view,  it  is  claimed  that 
care  must  be  exercised  to  avoid  using  so  much  water  as  to  "  drown  " 
the  cement,  and,  from  a  mechanical  standpoint,  voids  will  result 
through  evaporation  unless  means  be  provided  for  the  escape  of 
superfluous  water  during  induration.  This  is  usually  accom- 
plished in  plain  work  by  the  use  of  porous  molds,  while  in  orna- 
mental work,  by  the  process  of  casting  in  sand,  the  water  which 
is  not  consumed  by  the  internal  chemical  action  of  the  cement 
readily  finds  its  way  into  the  sand. 


CHAPTER  XI. 

FACING. 

THE  difficulty  of  obtaining,  by  molding  concrete  of  usual 
texture,  a  suitable  appearance  for  the  better  grade  of  exposed 
surfaces,  has  led  to  efforts  along  various  lines  looking  toward 
the  attainment  of  more  pleasing  surfaces.  Owing  to  the  board- 
forms  ordinarily  used  in  monolithic  construction  being  taken 
down  as  soon  as  the  concrete  will  retain  its  shape  -without  sup- 
port, the  practice  has  been  well-nigh  universal  in  that  class  of 
construction  to  plaster  a  rich  mixture  on  the  coarse  concrete 
immediately  after  removing  the  boards.  It  has  been  found 
that  adhesion  can  only  be  secured  by  roughening  the  surface 
of  the  set  concrete  with  a  wire  brush,  and  thoroughly  wetting 
this  roughened  surface  before  applying  the  facing.  Even  with 
these  precautions,  cases  are  frequent  in  which  the  contraction 
of  the  richer  mixture  during  the  setting  of  its  cement  has  caused 
cracks  and  resulted  in  separation  between  layers.  Another  objec- 
tion to  this  method  lies  in  the  troweling  incident  to  finishing, 
which  draws  the  cement  to  the  surface  and  results  in  hair-  or 
crazing- cracks. 

As  it  was  not  prudent  to  risk,  in  blocks  for  the  construction 
of  buildings,  such  dangers  as  have  been  mentioned,  it  was  not, 
in  the  earlier  stages  of  the  manufacture  of  concrete  blocks,  thought 
feasible  to  face  the  blocks  with  a  mixture  differing  from  the 
body  of  the  block.  Later  developments  have  shown  that  there 


52  CONCRETE-BLOCK  MANUFACTURE. 

are  other  methods  of  facing,  applicable  to  block-manufacture, 
which  eliminate  the  difficulties  attendant  upon  the  method  of 
facing  and  troweling  after  manufacture.  The  mixtures  com- 
monly used  for  facing  vary  from  1:1  to  1:3,  while  the  backing 
or  body  of  the  block  varies  from  1:4  to  1:3:4.  In  the  case  of 
blocks  tamped  in  an  upright  position,  one  side  of  the  mold  must 
needs  form  the  face;  and  the  only  way  of  applying  a  half-inch 
face  of  the  finer  material  is  by  the  insertion  of  a  partition  to 
separate  it  from  the  main  body  of  concrete.  It  is  evident  that 
this  leaves  a  distinct  line  of  cleavage  between  the  two  sections, 
and  does  not  insure  absolute  permanency.  It  is  becoming  quite 
common  to  make  blocks  face  down.  There  are  now  many 
machines  on  the  market,  adapted  to  the  latter  method  of  facing, 
which  contemplate  the  introduction  of  the  face-matter  first,  and 
its  thorough  tamping  against  the  face-plate  before  the  coarser 
concrete  is  deposited  in  the  mold.  In  this  way  the  partition  is 
eliminated  and  the  line  of  cleavage  less  marked.  In  the  manu- 
facture of  two-piece  blocks  under  pressure,  the  face-matter  is 
applied  in  the  top  of  the  mold  before  the  block  is  pressed;  and 
thus,  upon  subjection  to  heavy  pressure,  it  becomes  firmly 
imbedded  into  the  underlying  coarse  mass,  and  no  distinct  line 
of  cleavage  remains. 

It  has  been  generally  supposed  that  the  color  of  cement  had 
a  very  potent  influence  on  the  color  oL  the  face.  While  there 
is  an  element  of  truth  in  this  belief,  it  is  a  fact  that  the  color 
of  aggregate  and  the  purity  of  water  are  factors  more  worthy 
of  consideration.  In  many  block-factories,  cements  of  a  par- 
ticular color — usually  white — have  been  imported  from  France 
or  other  European  countries,  when  a  smaller  increase  in  cost 
would  have  obtained  an  aggregate  giving,  with  the  native  Port- 
land cements,  more  nearly  the  result  sought.  For  approxi- 
mately white  facing,  it  is  evident  that  white  sand  or  stone  screen- 


FACING.  53 

ings  should  be  used.  Irrespective  of  color,  however,  the  selec- 
tion and  preparation  of  sand  for  face-matter  is  of  the  greatest 
importance.  It  should  be  fine,  sharp,  of  a  hard  and  close  tex- 
ture, and  scrupulously  clean.  f  It  should  be  screened  imme- 
diately before  mixing,  not  only  to  remove  any  large  particles, 
but  to  loosen  it  up  as  much  as  possible,  so  that  the  mixing  may 
be  more  thoroughly  accomplished.  Owing  to  the  tendency  to 
stick  to  plates,  face-matter  is  usually  mixed  dryer  than  the  body 
of  the  block,  and,  as  it  is  always  a  rich  mixture,  there  is  a  slight 
tendency  to  roll  up  into  balls.  It  is,  therefore,  necessary  to  again 
screen  the  mixture  immediately  before  it  is  used. 

For  colored  work  the  best  practice  demands  the  use  of  screen- 
ings from  crushed  stone  of  the  desired  color.  Indeed,  this  is 
the  only  truly  correct  and  practicable  manner  of  obtaining  strong 
and  durable  colors  without  sacrificing  the  strength  of  the  block. 
There  are  but  few  plants  in  which  this  method  has  been  exten- 
sively used,  but  it  is,  nevertheless,  the  method  which  must  survive. 

There  are  several  firms,  now  manufacturing  various  colors 
for  block  work,  using  iron  pigments  as  a  base.  Of  course  it  is 
understood  that  vegetable  colors,  or  colors  containing  oils,  greases, 
or  acids,  cannot  safely  be  used  in  concrete  work.  Many  writers, 
have  undertaken  to  give  directions  for  the  use  of  ultramarine, 
ochre,  lampblack,  iron  oxide,  and  a  great  variety  of  other  color- 
ing matters.  The  facts  in  the  case  show  two  things:  First, 
that  all  colors  produced  by  such  artificial  means  are  liable  to  fade 
with  time;  second,  that  the  use  of  such  adulterants  in  quantity 
adequate  to  produce  the  desired  color,  with  sufficient  strength  to 
prevent  fading  for  a  reasonable  time,  weakens  the  concrete.  Gen- 
erally speaking,  it  is  probably  safe  to  say  that  an  unfading  color 
in  concrete  blocks  can  only  be  produced  by  use  of  an  aggregate 
of  the  required  color. 

In  facing  blocks  the  chief  end  sought,  aside  from  appearance, 


54  CONCRETE-BLOCK  MANUFACTURE. 

is  to  obtain  a  surface  approximately  water-tight.  The  fact  that 
only  fine  sand  is  used  decreases  the  size  of  voids  to  such  an  extent 
that,  by  the  use  of  a  large  proportion  of  cement,  the  face  (if 
mixed  reasonably  wet  and  properly  compacted)  may  be  made 
nearly  impermeable  without  the  use  of  any  chemical  adulterant. 
There  are,  however,  a  number  of  compounds  on  the  market,  for 
use  in  face-matter,  calculated  to  produce  a  perfectly  waterproof 
surface.  In  absence  of  information  as  to  their  ingredients,  it  is 
manifestly  impossible  to  express  an  opinion  either  as  to  their 
permanence  or  their  ultimate  effect  upon  the  cement. 

The  form  of  face  is  a  matter  of  the  particular  plates  used 
in  the  manufacture  of  blocks,  being,  in  the  case  of  upright  one- 
piece  blocks,  one  side  of  the  mold,  in  the  case  of  face-down  blocks 
the  bottom  of  the  mold,  and  in  the  case  of  two-piece  blocks  the 
pressing-plate.  In  supplying  these  plates,  it  has  been  the  usual 
custom  to  regard  pitch -face  as  a  standard  design.  That  it  is 
an  imperfect  imitation  of  the  cheapest  class  of  stone-work,  that 
it  lacks  the  boldness  and  variety  of  outline  found  in  the  original, 
and  that  it  robs  cement-work  of  its  own  intrinsic  merit,  does 
not  deter  the  block-maker  from  using  a  face  which  will  not  show 
the  imperfection  of  his  work  or  the  loose  texture  of  his  blocks, 
and  he  inflicts  upon  a  gullible  public  a  design  suitable  only  for 
basement  and  stable  construction.  Equally  culpable  and  inar- 
tistic is  he  who,  by  a  repetition  of  designs  produced  from  the 
same  face-plates,  destroys  the  decorative  possibilities  of  con- 
crete architecture  by  a  sucession  of  monotonous  ornamentation. 
The  manufacturer  of  machines,  the  block-maker,  and  the  archi- 
tect of  concrete-block  structures  will  alike  do  well  to  consider 
that  the  decorative  features  of  concrete  blocks  lie  not  less  in 
plain  and  imposing  walls  than  in  contrasting  ornamentation* 
They  may  also  remember  that  the  value  of  ornamentation  is 
enhanced  by  beautiful  walls  of  blocks  that  are  plain,  or  by  blocks 


FACING.  55 

that  are  beveled  to  emphasize  mortar-joints,  after  the  manner 
of  the  rusticated  exteriors  of  the  Italian  renaissance,  with  which 
tool-face  blocks  may  be  suitably  interpolated.  Such  architecture 
will  carry  concrete  blocks  into  structures  where  they  could  never 
go  by  the  prevalent  use  of  a  dull,  plastic-like  imitation  of  hewn 
stone,  or  a  motley  conglomeration  of  inartistic  ornamentation. 


CHAPTER  XII. 

ORNAMENTATION. 

As  suggested  in  the  previous  chapter,  ornamentation  should, 
in  concrete-block  buildings,  be  a  contrasting  decorative  feature. 
It  is  therefore  evident  that  in  quantity  and  size  it  constitutes, 
in  truly  artistic  construction,  but  a  small  proportion  of  the  build- 
ing; and  it  may  be  fairly  assumed  that  its  production  warrants 
a  manufacturing  cost  which  would  be  beyond  reason  for  the 
main  portion  of  the  walls.  This  statement  is  further  emphasized 
by  the  fact  that  such  ornamentation  is  successfully  replacing  a 
good  quality  of  hand-cut  natural  stone,  the  cost  of  which  is  far 
beyond  that  of  ornamental  cement-work  produced  by  any  process. 

In  considering  the  methods  by  which  ornamentation  may  be 
produced  we  may,  for  reasons  stated  in  Chapter  XI,  pass  those 
designs  furnished  with  a  number  of  machines,  whose  manu- 
facturers have  modified  the  egg-and-dart  and  a  few  other  standard 
ornamental  features  by  eliminating  the  undercut,  and  who  fur- 
nish iron  plates  cast  from  such  patterns. 

Fig.  12  shows  ornamental  work  manufactured  for  the  Chicago 
Drainage-canal  Power-house,  near  Lockport,  111.  The  process 
used  in  producing  this  work  involved  the  casting  of  plaster  molds 
from  patterns.  The  cement  was  poured  into  these  molds,  and, 
owing  to  the  undercut,  the  molds  were  broken  after  the  cement 
had  hardened.  Of  course,  where  there  is  no  undercut  the  molds 
can  be  made  in  sections  and  removed  without  breakage. 

56 


ORNAMENTATION. 


57 


One  very  large  company  of  ornamental  workers  employs 
sectional  wooden  molds  almost  exclusively.  These  must  be 
thoroughly  shellacked  to  prevent  warping  and  cracking. 

Glue  molds  have  been  extensively  used  in  the  finer  lines  of 
ornamental  cement-work.  A  well-molded  glue  negative  may 
be  used  about  twenty  times,  as  its  elasticity  permits  removal 
from  work  having  a  considerable  undercut. 


FIG.  12. — Ornamental  Work  for  Chicago  Drainage-canal  Power-house. 


Casting  in  sand  seems  to  be  the  easiest  and,  all  things  con- 
sidered, the  most  inexpensive  method  of  producing  thoroughly 
satisfactory  ornamental  work.  As  it  requires  merely  a  wooden 
pattern,  iron-molders'  sand,  and  wet  concrete,  it  is  evident  that 
a  high  degree  of  skill  is  not  essential  to  perfect  work.  The  only 
item  of  great  expense  is  the  pattern,  and  this  may  often  be  secured 


5  8  CONCRETE-BLOCK  MANUFACTURE. 

in  natural  stone  or  some  other  material,  if  of  a  design  not  obtain- 
able in  wood,  without  the  services  of  a  pattern-maker. 

It  is  but  fair,  to  that  one  who  is  about  to  embark  in  the  busi- 
ness of  manufacturing  and  selling  concrete  blocks,  to  state  that 
he  should  not  undertake  elaborate  ornamental  work  without 
long  experience  in  the  more  easy  departments  of  concrete  manu- 
facture. The  manufacture  of  ornamental  work  is  distinctly 
a  separate  branch  of  the  cement  industry,  and  one  requiring 
great  skill.  The  ease  with  which  cement  assumes  any  desired 
form,  and  the  beautiful  effects  produced  by  the  skillful  oper- 
ator, lead  the  novice  to  tread  on  most  dangerous  ground.  It  is 
one  thing  to  make  an  ornament,  and  quite  another  thing  to  pro- 
duce one  that  will  stand  the  test  of  time.  The  sharp  arrises, 
the  fine  lines,  and  the  intricate  designs  of  desirable  ornamenta- 
tion require  a  degree  of  familiarity  with  the  action  of  cement, 
both  in  molding  and  in  exposure  to  atmospheric  influences, 
which  is  too  often  gained  by  the  loss  of  a  customer's  goodwill. 
Above  all  things,  the  common  practice  of  employing  chemicals 
for  accelerating  the  set  of  cement,  in  the  production  of  orna- 
mental designs,  is  to  be  deprecated  as  irreparably  harming  the 
business  of  the  future. 


CHAPTER  XIII. 

CURING. 

THERE  can  be  no  greater  error  in  block-making  than  to  con- 
sider the  process  of  manufacture  complete  when  a  block  is  taken 
from  the  mold.  It  is  in  the  application  of  scientific  methods 
to  the  subsequent  induration  of  the  block  that  this  style  of  con- 
struction possesses  a  marked  advantage  over  monolithic  con- 
crete construction.  It  is  in  the  adaptability  of  concrete  blocks 
to  thorough  curing  before  laying  that  they  are  capable  of  acquir- 
ing that  degree  of  strength  and  durability  which  is  ultimately 
destined  to  place  them  in  the  first  rank  as  a  building  material. 
It  must  not,  however,  be  supposed  that  the  mere  setting  away 
to  cure,  or  allowing  to  dry,  constitutes  what  is  rightly  embraced 
in  the  comprehensive  process  termed  curing.  It  rather  involves 
a  most  careful  application,  during  a  series  of  days,  of  scientific 
methods  calculated  to  give  quality  to  the  product,  and  it  is  to  a 
neglect  of  such  methods  that  most  failures  in  block-making  are 
attributable. 

As  is  well  known,  cement  is  the  bonding  element  of  con- 
crete, and  its  value  in  that  regard  lies  wholly  in  its  hydraulicity. 
As  mentioned  in  a  previous  chapter,  crystallization  is  the  result 
of  hydration,  and  thorough  crystallization  is  only  effected  by 
the  use  of  a  considerable  quantity  of  water.  It  must  be  still 
further  considered  that  crystallization  is  by  no  means  an  instan- 

59 


60  CONCRETE-BLOCK  MANUFACTURE. 

taneous  process;  that  only  what  is  commonly  termed  the  initial 
set  is  secured  by  the  admixture  to  the  cement  and  aggregate  of 
the  amount  of  water  most  commonly  used  in  molding  blocks; 
and  that  reliance  must  be  had  upon  subsequent  addition  of 
moisture  to  secure  that  later  crystallization  without  which 
blocks  are  worthless  for  practical  purposes. 

Maintenance  of  uniform  conditions  is  the  keynote  to  suc- 
cessful curing.  It  is  absolutely  essential  that  blocks  shall  not, 
during  the  period  of  curing,  be  exposed  to  the  sun.  The  reason 
for  this  becomes  apparent  if  a  freshly-made  block,  thoroughly 
saturated  with  water,  be  exposed  for  a  few  hours  to  the  direct 
rays  of  the  sun.  It  will  be  noted  that  one  side  becomes  very 
dry  while  the  other  remains  moist;  and  the  exposed  side  will 
show  a  baked  appearance,  and,  by  the  rapidity  of  contraction, 
develop  checks  and  shrinkage-cracks,  while  serious  structural 
cracks  are  liable  to  result  in  the  interior  of  the  block,  owing  to 
the  variance  in  rate  of  contraction  between  the  front  and  back. 
It  may  here  be  noted  that  a  large  percentage  of  cracks,  both 
structural  and  surface,  are  caused  by  rushing  green  blocks  into 
a  wall.  Many  operators  have,  in  their  earlier  experience,  made 
the  mistake  of  placing  in  a  wall  blocks  only  three  or  four  days 
old ;  and  the  results,  especially  if  the  wall  be  exposed  to  the  sun, 
have  fully  justified  a  sweeping  condemnation  of  such  practice. 
It  will  ever  be  a  source  of  mortification  to  the  block-maker  if  he 
allows  the  insistence  of  a  builder,  who  is  anxious  for  blocks  on 
a  certain  day,  to  lead  him  to  deliver  partially  cured  blocks  to 
be  used  above  ground. 

The  main  element  in  curing,  under  methods  now  commonly 
in  use,  is  water,  and  it  should  be  applied  at  such  intervals  and 
in  such  manner  that  the  condition  of  moisture  will  at  all  times 
be  uniform.  This  may  be  secured  by  sprinkling  the  blocks 
thoroughly  three  or  four  times  a  day.  The  amount  of  water 


CURING.  6 1 

and  the  frequency  with  which  it  should  be  applied  are  dependent 
to  a  great  extent  upon  weather  conditions.  It  is  evident  that  in 
cold  weather,  or  in  a  humid  atmosphere,  sprinkling  may  occur 
at  less  frequent  intervals  than  would  be  necessary  in  a  dry  climate 
or  in  very  hot  weather.  Sprinkling  should  begin  as  soon  as 
the  blocks  have  attained  sufficient  rigidity  that  a  fine  spray  will 
not  deface  the  surface.  If  a  dry  mixture  has  been  used,  it  is 
evident  that  a  larger  amount  of  water  will  be  consumed  than 
will  be  the  case  where  blocks  have  been  made  of  a  medium  or 
a  wet  mixture.  In  the  former  case,  blocks  should  be  kept  thor- 
oughly moist  for  at  least  twenty  days,  while  in  the  latter  case 
ten  days  will  suffice.  A  rule  which  should  not  be  violated  under 
any  circumstances  is  that  blocks  of  dry  mixture  require  minimum 
curing  of  fifteen  days,  and  blocks  of  medium  mixture  require 
minimum  curing  of  seven  days.  The  sprinkling  shoulol  be  so 
thorough  that  no  portion  of  any  block  will  turn  white ;  and  espe- 
cial attention  should  be  given  to  any  ornamental  designs,  as  well 
as  to  corners,  which  usually  dry  faster  than  the  main  surface. 
To  maintain  uniformity  of  moisture,  it  will  be  found  useful  to 
protect  the  blocks  with  hay,  excelsior,  burlap,  or  any  substance 
which  will  serve  to  retain  moisture.  By  first  thoroughly  wetting 
a  pile  of  blocks,  covering  in  this  manner,  and  then  keeping  the 
covering  matter  thoroughly  wet,  the  loss  of  moisture  otherwise 
obtaining  may  be  prevented,  and  the  blocks  be  constantly  sur- 
rounded by  uniformly  moist  air. 

A  circulation  of  air  is  desirable  as  between  and  among  the 
blocks ;  and  not  only  for  this  reason,  but  also  to  prevent  discolor- 
ation, blocks  should  not  come  in  contact  with  one  another,  but 
tiers  should  be  arranged  so  that  a  slight  air-space  will  intervene, 
and  layers  should  be  separated  by  laths  laid  between.  In  this 
connection  it  may  be  noted  that  uniform  color  can  only  be  obtained 
by  uniform  curing.  The  influence  of  curing  upon  color  is  a 


62  CONCRETE-BLOCK  MANUFACTURE. 

matter  which  has  not  been  given  so  serious  consideration  as  it 


FIG.  13. — Full  Set  of  Molds  and  Accessories  forming  a  Simple  Equipment  of  the 

Roll-over  Type. 

deserves,  for  it  is  a  most  essential  factor  in  securing  that  uni- 
formity of  appearance  so  much  desired. 


CURING.  63 

Steam-curing  of  blocks  is  a  matter  in  which  considerable 
interest  is  manifested  at  this  time.  It  is  of  course  well  under- 
stood that  placing  blocks  in  live  steam  will  effect  an  apparently 
thorough  cure  in  an  incredibly  short  time;  but  the  experiments 
along  this  line  have  been  so  few,  and  the  statements  of  actual 
results  observed  during  any  considerable  period  of  time  are  so 
limited,  that  the  expression  of  decided  views  on  the  subject  is 
not  yet  justified.  It  is,  however,  interesting  to  note  that,  in  the 
construction  of  a  very  large  public  building  in  the  State  of  New 
York,  the  local  company  which  is  manufacturing  the  blocks  is 
also  the  owner  of  a  sand-lime  brick-plant,  and  has,  in  the  steam- 
cylinder  of  the  latter  plant,  cured  blocks  so  effectively  that  when 
forty-eight  hours  old  they  have  been  placed  in  the  wall  beside 
blocks  cured  for  the  customary  time  by  usual  methods.  It  is 
the  present  belief  that  the  best  results  in  steam-curing  are  obtained 
by  exposing  the  blocks  in  thoroughly  moist  air  for  twenty-four 
hours  before  subjecting  them  to  steam,  thus  following  standard 
practice  for  accelerated  tests  of  cement  briquettes. 

Curing  in  freezing  weather  is  difficult,  but  not  impossible. 
The  blocks  must  be  kept  from  freezing  for  the  first  four  or  five 
days  to  avoid  expansion-cracks  caused  by  swelling  from  freezing. 
At  the  end  of  that  time  sufficient  firmness  should  have  been 
attained  to  withstand  the  tendency  to  expansion;  and  in  that 
case  no  damage  will  result,  as  freezing  only  suspends  crystalliza- 
tion, and  a  subsequent  rise  in  temperature  causes  a  resumption 
of  the  chemical  process. 


CHAPTER  XIV. 

MACHINES. 

IN  considering  machines  and  molds  for  the  manufacture 
of  concrete  blocks  it  will  be  well  to  divide  them  into  three  groups 
and  consider  them  in  the  following  order: 

1.  Machines    and    molds    for    manufacturing    blocks    by 
tamping   a   dry   mixture,   using   a   comparatively  fine 
aggregate. 

2.  Machines  for  compressing  in  molds,  without  tamping,  a 
medium-wet  mixture,  using  an  aggregate  graded, from 
fine  to  coarse. 

3.  Molds  for  forming  blocks  by  pouring  a  wet  mixture. 

It  must  be  understood  by  the  reader  that  this  classification 
is  to  a  certain  extent  arbitrary,  and  that  there  are  certain  points 
where  the  various  classes  overlap.  It  must  also  be  understood 
that  the  list  of  machines  illustrated  or  described  is  not  submitted 
as  complete.  The  limitations  of  this  work  by  no  means  per- 
mit of  a  description  of  each  machine  on  the  market,  but  it  has 
been  the  intention  to  select  such-  machines  as  exemplify  certain 
principles  of  manufacture;  and  the  same  principles  are  in  many 
cases  embodied,  with  slight  mechanical  changes,  in  a  large  num- 
ber of  various  makes.  Neither  is  it  claimed  that  the  description 
sets  forth  all  particulars  relative  to  the  operation  of  any  particu- 
lar style.  These  particulars  are  readily  ascertainable  from 
t  manufacturers'  catalogues,  and  it  is  very  far  from  the  purpose 

64 


MACHINES. 


to  make  this  work  .in  any  sense  a  compilation  of  catalogue  litera- 
ture. It  is  rather  the  purpose  to  present  some  of  the  more  marked 
peculiarities  of  the  various  types,  and  to  mention  some  of  their 
more  patent  points  of  relative  merit  and  demerit. 


FIG.  14. — Upright  Machine  with  Drop  Cores. 

The  objects  of  a  concrete-block   mold  or  machine  are  six: 

1.  Means  for  enclosing  the  mass  during  formation   into 

desired  shape  and  size. 

2.  Means  for  properly  and  quickly  compacting  the  mass. 


66  CONCRETE-BLOCK  MANUFACTURE. 

3.  Means  for  giving  desired  variation  to  exposed  surfaces. 

4.  Means  for  making  a  face  of  texture  differing  from  the 

body  of  the  block. 

5.  Means  for  rapid  discharge  of  the  product. 

6.  Means  for  preventing  injury  to  the  block  while  green. 
All  of  the  six  factors  mentioned  may  fairly  be  said  to  be 

entitled  to  consideration  in  every  machine,  and  the  various 
machines  show  the  result  of  attention  directed  especially  to  one 
or  another  of  them. 

In  Fig.  13  is  shown  a  full  set  of  cores,  plates,  and  the  like, 
comprising  a  medium-price  outfit  of  the  roll-over  type.  In  oper- 
ating this  outfit  the  plate  to  which  the  cores  are  attached  is  set 
on  a  level  surface  or  working-table  of  convenient  height;  the 
plates  comprising  the  sides  and  ends  are  selected  according  to 
the  particular  design  desired  for  the  surface  of  the  block  and 
are  clamped  in  place.  The  mold  is  then  partly  filled  and  the 
mixture  tamped,  this  filling  and  tamping  being  repeated  until 
the  mold  is  heaped  slightly  above  the  sides.  The  mixture  in 
the  mold  is  then  leveled  with  a  straight-edge,  and  a  board  some- 
what larger  than  the  block  put  on  top.  The  whole  apparatus 
is  then  turned  over  so  that  the  mold  rests  on  the  board.  The 
iron  plate  is  now  lifted  straight  up,  withdrawing  the  cores  with 
it;  the  sides  of  the  mold  are  undamped  and  removed,  and  the 
block  is  set  away  to  cure  on  the  board. 

In  Fig.  14  is  shown  an  upright  machine  upon  a  metal  stand, 
being  the  latest  model  of  one  of  the  first  manufacturers  of  block 
machines.  The  especial  feature  of  this  machine  is  the  dropping 
of  the  cores  out  of  the  block  after  it  has  been  tamped.  Simul- 
taneously with  the  dropping  of  cores  the  sides  are  opened,  as 
shown  in  Fig.  15,  and  the  block  removed  on  an  iron  pallet  of 
the  shape  and  size  of  the  block  itself,  and  having  openings  corre- 
sponding to  the  cores  and  hollow  spaces.  This  type  of  machine 


MACHINES.  67 

has  been  very  closely  imitated  by  many  manufacturers  who  have 
entered  the  field  in  later  years.  The  variations  which  they  have 
made  from  the  original  have  been  calculated  to  secure  greater 
facility  of  operation,  or  to  attain  greater  efficiency  in  some  one 


FIG.  15. — Upright  Machine  Releasing-block. 

of  the  essential  points  mentioned  in  opening  this  chapter.  It 
appears,  however,  that  the  recent  improvements  embodied  in 
this  machine  are  well  calculated  to  enable  it  to  maintain  its  posi- 
tion of  supremacy  among  the  upright  machines.  Despite  the 
efforts  of  its  imitators  to  belittle  its  efficiency,  it  must  be  acknowl- 


68 


CONCRETE-BLOCK  MANUFACTURE. 


edged  that  its  product  is  uniformly  excellent,  and  that  many 
worthy  buildings   stand  to  its  credit. 


FIG.  16. — Moving  the  Mold  rather  than  the  Block. 

In  the  mold  illustrated  in  Fig.  16  the  point  of  preserving  the 
block  from  deformation  while  green  has  been  emphasized  by 


MACHINES. 


69 


leaving  the  block  on  the  ground  where  made  and  removing  the 
mold  from  the  block,  thus  relieving  the  block  from  any  jar  in 
handling  until  it  has  become  somewhat  hard. 

Fig.  17  shows  a  machine  in  which  the  characteristic  feature 


is  facility  of  facing.  There  are  many  machines  now  manu- 
factured embodying  the  same  general  principle  shown  in  the 
illustration.  They  are  commonly  termed  face-down  machines, 
and  use  the  plate  forming  the  outer  surface  of  the  block  as  the 


70  CONCRETE-BLOCK  MANUFACTURE. 

bottom  of  the  mold,  on  which  the  fine  facing  matter,  varying  from 
i :  i  to  1:3  mixture  of  cement  and  fine  sand,  granite  screenings 
or  marble  dust,  is  deposited  and  thoroughly  tamped,  after  which 
the  leaner  mixture  comprised  in  the  body  of  the  block  is  deposited 
and  tamped  in  the  usual  manner,  except  that  the  cores,  which  it 
will  be  noted  enter  and  withdraw  laterally,  are  not  inserted  until 
the  lower  half  of  the  block  has  been  tamped  to  place.  In  most 
machines  of  this  type  the  mold  is  so  arranged  that,  when  the 
block  is  ready  for  delivery,  the  mold  may  be  turned  to  an  upright 
position  and  the  block  released  either  on  a  wooden  pallet  or 
on  an  iron  bottom-plate  in  the  manner  described  in  connection 
with  the  upright  machines. 

In  Fig.  1 8  is  shown  a  machine  which  was  originally  of  the 
upright  type,  on  which  the  manufacturers  later  arranged  a  device 
for  tilting  to  an  angle  of  45°  to  admit  of  depositing  face-matter 
without  the  use  of  a  partition,  and  which,  by  still  later  improve- 
ment of  the  tilting  device,  has  been  brought  into  direct  com- 
petition with  face-down  machines  by  the  latest  model,  as  shown 
in  the  illustration,  which  still  preserves  all  the  advantages  of 
the  upright  type.  The  mechanical  feature  of  this  machine 
which  claims  attention  is  the  raising  and  lowering  of  the  bed- 
plate upon  stationary  cores,  and  the  engaging  of  side  and  end 
plates  by  a  frame  which  throws  the  mold  into  position  for  refill- 
ing as  the  bed-plate  drops  into  position. 

In  Fig.  19  is  shown  a  mechanical  press  for  manufacturing 
two-piece  blocks  from  a  medium-wet  mixture  in  which  a  coarse 
aggregate  is  employed.  As  it  is  the  perfection  of  this  machine 
which  has  brought  two-piece  blocks  into  the  extensive  use  which 
they  now  enjoy,  and  as  the  method  of  operation  is  in  every  respect 
at  variance  from  the  machines  already  described,  it  may  be  inter- 
esting to  consider  in  some  detail  the  process  of  making  pressed 
blocks.  It  will  be  noted  that  the  pressure  is  applied  by  means 


MACHINES.  7  * 

of  upright  hand-levers,  which,  by  lowering  either  to  the  right 
or  to  the  left,  bring  into  action  an  arrangement  of  compound 
toggles  which  exert  upon  the  movable  bed  of  the  press  a  pressure 


FIG.   1 8. —Combination  Upright  and  Face-down  Machine. 

of  60,000  pounds.  The  molds  are  filled  at  their  respective  ends 
of  the  track,  the  medium-wet  mixture  of  one  part  cement,  three 
of  sand,  and  four  of  gravel  or  broken  stone  being  shoveled  into 
the  mold  and  raked  off  level.  If  it  is  desired  that  the  face  be 


?2  CONCRETE- BLOCK  MANUFACTURE. 

of  fine  texture,  a  gauge  is  used  at  this  stage  of  the  process,  raking 
from  the  top  of  the  mold  a  quarter  or  half  inch  of  the  coarse 
mixture,  and  a  half-shovelful  of  fine  face-matter,  previously 
screened  to  avoid  lumps,  is  applied.  The  pressing-plate  of  the 
particular  design  required  is  then  put  in  place  on  top  of  the 
mold,  and  the  mold,  which  is  hung  on  trolleys  having  grooved 
wheels  fitting  the  track,  is  then  run  into  the  press  and  the  pres- 


FiG.   19. — Mechanical  Press  making  Two-piece  Blocks. 

sure  made.  From  three  to  four  seconds  is  required  in  this  oper- 
ation. As  the  pressure  is  relieved,  the  mold  is  withdrawn  and 
two  hooks  thrown  over  the  pressing-plate  to  hold  it  in  place, 
while  the  mold  is  inverted  and  run  to  the  end  of  the  track.  The 
releasing-stand,  which  is  shown  below  the  mold  in  the  illustra- 
tion, is  then  raised  to  engage  the  pressing-plate,  the  hooks  loosened, 
and  the  block  lowered  (face  down),  resting  on  the  plate  by  which 
it  was  pressed.  The  process  is  very  rapid,  expert  men  pro- 


MACHINES.  73 

duoing  unfaced  blocks  in  twenty  seconds  and  faced  blocks  in 
thirty.  The  making  of  corner,  jamb,  and  other  special  blocks 
requires  somewhat  more  time.  Corner  returns  are  faced  by 
tilting  the  mold  to  admit  the  face-matter  on  the  return,  and  the 
pressure  on  the  return  is  given  by  an  ingenious  interior  bevel 
which  crowds  the  mass  endwise.  It  should  be  especially  noted 
that  this  machine  is  peculiarly  adapted  for  manufacturing  two- 
piece  blocks,  as  it  exerts  the  pressure  directly  on  the  face  of 
the  block;  also  that  two-piece  blocks  are  peculiarly  adapted 
for  manufacture  in  this  machine,  as  they  have  no  interior  cores, 
and  can  therefore  be  released  from  the  mold  face  down.  It  should 
be  stated  that  the  molds  are  provided  with  numerous  vent-holes, 
which  permit  the  escape  of  air  when  pressure  is  applied  and 
admit  air  while  releasing,  thus  obviating  the  creation  of  a  vacuum 
behind  the  block.  A  number  of  different  castings  which  are 
commonly  termed  cores,  but  are  not  interior  cores,  are  provided 
for  making  many  different  shapes  and  sizes  of  blocks,  the  range 
in  width  extending  from  the  thinnest  partition  to  a  seventeen- 
inch  wall,  all  being  made  in  the  same  mold  by  adjustable  cores 
and  fillers. 

The  poured  system  admits  of  the  use  of  a  variety  of  different 
materials  in  the  molds.  The  fact  that  compression  is  eliminated, 
and  that  the  block  becomes  compact  by  the  mere  settlement 
of  the  fluid  mixture,  makes  it  unnecessary  for  the  molds  to  resist 
any  severe  strain.  For  this  reason,  and  because  of  its  ability 
to  take  up  the  superfluous  moisture  in  the  mixture,  sand  is  well 
adapted  for  such  molds;  and  the  process  of  casting  in  sand,  as 
described  in  a  previous  chapter,  has  given  rather  better  results 
than  has  the  use  of  any  other  kind  of  mold.  Wooden  molds 
may  be  used,  providing  the  wood  be  thoroughly  waterproofed 
to  prevent  warping.  Some  two  or  three  years  ago  a  system 
of  sheet-iron  molds  was  placed  on  the  market  for  making  blocks 


74  CONCRETE-BLOCK  MANUFACTURE. 

by  the  poured  process.  The  molds  are  well  adapted  to  the  pur- 
pose, and  have  been  installed  in  a  considerable  number  of  fac- 
tories; but  the  fact  that  the  natural  gravitation  of  heavier  por- 
tions of  the  mass  to  the  bottom  causes  lack  of  uniformity  through- 
out the  block,  and  the  difficulty  of  producing  a  satisfactory  face, 
have  served  as  obstacles,  while  the  long  time  which  the  molds 
are  retained  in  service  before  blocks  can  be  removed,  and  the 
consequent  large  number  of  molds  required  for  producing  any 
considerable  output  of  product,  have  greatly  hindered  the  popu- 
larization of  these  molds. 


OF  THF 

UNIVERSITY 

OF 


CHAPTER  XV. 

PLANT   ARRANGEMENT. 

IN  the  location,  designing,  and  equipping  of  a  plant  the  first 
requisite  is  ample  ground-space,  which  should  be  located  close 
to  market.  The  plant  should  be  within  a  reasonable  hauling 
distance  of  that  section  in  which  it  is  anticipated  that  the  majority 
of  buildings  of  block  construction  will  be  located.  One  is  inclined 
to  feel  that  the  essential  thing  in  choosing  a  location  is  to  get 
near  the  sources  of  supply  of  the  raw  materials,  and  hence  make 
the  mistake  of  locating  a  plant  at  a  gravel-bank,  or  near  a  stream 
from  which  sand  and  gravel  may  be  procured,  overlooking  the 
long  haul  entailed  on  the  finished  product.  Unlike  most  con- 
tract work,  it  will  be  found  much  cheaper  to  haul  the  raw  mate- 
rials for  block-manufacture  than  to  haul  the  finished  product. 
Great  care  must  be  exercised  in  the  transportation  of  blocks 
from  the  factory  to  the  building-site  in  order  to  prevent  breakage 
and  defacement.  It  must  be  remembered  that  the  tiniest  chip 
from  the  corner  of  a  block  often  means  to  a  conscientious  oper- 
ator, and  not  less  to  one  who  cares  for  future  business,  a  total 
loss  of  the  block.  Hence  a  long  haul  on  raw  materials  and 
a  short  haul  on  blocks  is  preferable  to  a  short  haul  on  the  former 
and  a  long  haul  on  the  latter.  If  possible  to  secure  trackage  it  is 
a  great  advantage,  both  as  to  receiving  cement  and  such  special 

75 


76  CONCRETE-BLOCK  MANUFACTURE. 

character  of  aggregate  as  may  occasionally  be  necessary,  and  as 
to  shipping  blocks  to  outside  points  in  contiguous  territory. 

In  caring  for  freshly-made  blocks  it  is  necessary,  except 
under  processes  leaving  the  blocks  on  the  ground,  that  they 
should  be  racked.  In  small  plants,  racks  for  this  purpose  may 
be  conveniently  arranged  by  making  for  the  ends  and  center  of 
the  rack  a  frame  of  2"X6"  lumber  and  placing  thereon  2"X4" 


FIG.  20. — Car  Suitable  for  Concrete  Blocks. 

stringers.  The  latter  should  not  be  nailed,  but  should  be  put  in 
place  as  required,  so  that  the  off-bearers  may  have  ample  room 
for  setting  blocks  on  the  stringers,  and,  as  each  tier  of  blocks 
is  in  place,  the  stringers  for  the  next  higher  tier  are  put  on  the 
rack.  For  large  factories,  however,  it  is  much  better  to  pro- 
vide cars  for  the  product.  In  Fig.  20  a  convenient  type  is  shown. 
These  may  be  obtained  in  various  sizes  suited  to  the  particular 
type  of  blocks  manufactured,  or  trucks  may  be  purchased  and 


PLANT  ARRANGEMENT. 


77 


the  cars  built  up  of  rough  lumber,  according  to  individual  require- 
ments. Tracks  may  be  constructed  of  hard  wood  or  of  light 
T-rail,  and  should  run  from  the  machine  to  the  curing- yard.  It 
is  a  frequent  practice  to  have  considerable  trackage  in  the  shed 
adjoining  the  manufacturing-room,  and  to  keep  the  blocks  on 
the  cars  for  several  days  before  exposing  them  in  the  open  curing- 


FIG.  21. — System  of  Cars  and  Tracks. 

yard.  In  that  case  it  becomes  necessary  to  have  a  transfer- 
car  for  switching  the  regular  cars  from  one  track  to  another, 
consisting  merely  of  a  wheeled  truck  on  a  sunken  track  running 
at  a  right  angle  to  the  surface  tracks.  In  Fig.  21  such  a  transfer- 
track  is  shown  in  the  foreground.  The  cars  shown  in  this  illus- 
tration consist  of  wood  frames  built  upon  iron  trucks.  In  this 
system  of  tracks,  second-hand  street-car  rails  were  utilized.  The 


73  CONCRETE-BLOCK  MANUFACTURE. 

cars  should  sit  very  close  to  the  machine  while  blocks  are  being 
manufactured,  as  an  enormous  amount  of  time  is  usually  con- 
sumed in  off-bearing  owing  to  lack  of  proper  convenience  of 
cars  or  racks. 

Doubtless  the  most  convenient  and  economical  arrangement 
for  handling  materials  is,  where  circumstances  permit,  to  have 
overhead  sand-  and  gravel-bins  discharging  into  the  mixer,  with 
the  mixer  elevated  so  that  it  will  discharge  on  a  platform  of  such 
height  that  the  concrete  may  be  readily  raked  into  the  mold. 
If,  however,  the  contour  of  the  ground  renders  such  an  arrange- 
ment impracticable,  the  same  result  may  be  obtained  by  the 
use  of  inclined  belt-conveyors,  which  will  be  found  the  most  sat- 
isfactory means  for  elevating  and  transporting  concrete. 

Of  course  either  one  of  the  elaborate  arrangements  men- 
tioned in  the  last  paragraph  will  not  be  installed  in  the  small 
plant,  but  it  is  not  of  less  importance  for  the  smallest  operator 
to  carefully  arrange  his  plant  with  a  view  of  securing  the  great- 
est compactness  and  convenience.  The  bins  should  be  close  to 
the  mixing-platform,  and  the  mixing-platform  close  to  one  side 
of  the  machine,  with  racks  readily  accessible  on  the  other  side. 

There  are  now  few  places  where  sufficient  water-pressure 
to  use  a  hose  is  not  obtainable,  and  the  application  of  water  from 
a  hose-nozzle  is  far  preferable  and  more  uniform  than  any  other 
method.  In  the  large  yards  it  is  customary  to  save  labor  by 
running  a  water-pipe  around  the  curing-yard,  having  automatic 
lawn-sprinklers  at  intervals  for  wetting  stacks  of  blocks. 

The  curing-yard  is  an  important  consideration,  and  must 
be  comparatively  large.  It  should  be  protected  by  a  roof  under 
which  the  blocks  may  remain  until  curing  is  nearly,  if  not  quite, 
completed.  In  winter  it  will  become  necessary  to  enclose  the  sides, 
and  this  may  be  cheaply  done  with  blocks.  If  desired,  these 
blocks  may  be  laid  in  lime-mortar,  and  taken  down  in  the  spring 


PLANT  ARRANGEMENT.  79 

for  use  in  other  construction.  During  the  past  winter  one  rail- 
road company  successfully  operated  on  this  plan,  heating  the 
temporary  building  by  means  of  a  large  cannon-stove  in  either 
end  and  placing  the  machine  midway,  with  blocks  stacked  at 
the  ends. 


CHAPTER  XVI. 

PLANT  EMPLOYEES. 

One  of  the  most  important  factors  in  the  success  of  a  con- 
crete-block plant  is  a  foreman  of  intelligence,  experience,  and 
character.  The  oft-repeated  statement  of  manufacturers  of 
block  machines,  that  the  commonest  kind  of  common  labor  can 
produce  the  best  concrete  blocks,  is,  to  use  the  mildest  language 
possible,  misleading.  It  is  to  belief  in  this  statement  that  a 
considerable  number  of  block-makers  might  justly  charge  their 
failure  to  introduce  blocks  into  their  community,  as  well  as 
their  pecuniary  loss.  It  is  to  the  result  of  this  erroneous  advice 
that  manufacturers  may  charge  the  failure  of  their  salesmen 
to  place  machines  in  many  towns  adjacent  to  those  where  failures 
have  occurred.  The  foreman  of  a  concrete-block  factory  must 
possess,  in  a  marked  degree,  those  qualities  of  sterling  character 
which  make  one  a  handler  of  men:  he  must  have  the  capacity 
to  systematize  their  duties  and  to  accomplish  results,  and  in 
addition  to  this  ability  he  must  know  the  nature,  uses,  and  limita- 
tions of  cement ;  and  he  must  be  especially  versed  in  the  theory 
and  practice  of  mixtures,  proportioning,  aggregates,  voids,  and 
general  concreting.  He  must  so  thoroughly  understand  the 
particular  machine  in  use  and  the  materials  locally  available 
that  he  will  obtain  the  maximum  of  quality  in  his  product  under 

all  conditions.     He  must  know  something  of  building  construe- 
So 


PLANT  EMPLOYEES.  81 

tion  and  architecture,  and  must  be  able  to  take  a  set  of  work- 
ing drawings  and  therefrom  manufacture  each  block  to  fit  its 
appointed  place.  He  must  be  a  judge  of  the  capacity  of  a  block 
to  withstand  the  strain  placed  upon  it,  and  be  able  to  deter- 
mine what,  if  any,  reinforcement  may  be  necessary  to  afford  a 
requisite  factor  of  safety.  With  such  a  foreman,  a  block  plant 
cannot  fail. 

The  mold-maker,  who  in  smaller  plants  may  be  the  foreman, 
must  be  able  to  manufacture  from  lumber,  with  or  without  a 
lining  of  galvanized  iron,  molds  for  such  special  members  in 
building  construction  as  are  beyond  the  dimension  capacity  of 
the  machine  in  use,  and  for  such  special  shapes  of  blocks  as  may 
be  required  to  suit  the  plans  of  the  architect,  and  for  which  pro- 
vision has  not  been  made  in  the  adjustability  of  the  block  machine. 
In  the  latter  case,  it  is  often  unnecessary  to  construct  an  entire 
mold,  but  the  regular  mold  may  be  used  by  the  insertion  of  fillers. 
It  must  be  understood  that,  however  thoroughly  the  designer 
of  a  block  machine  may  anticipate  the  many  special  shapes  and 
sizes  incident  to  all  kinds  of  construction,  it  is  impossible  for 
him  to  foresee  all  the  various  modifications  that  may  be  intro- 
duced by  individual  architects  unfamiliar  with  block  construction ; 
and  the  up-to-date  block  factory  must  be  able  to  earn  the  approval 
of  architects  by  building  to  their  specifications  rather  than  requir- 
ing their  specifications  to  fit  an  arbitrary  size  or  design  of  blocks. 
It  is  rarely  understood  by  block-makers  how  easy  this  accom- 
plishment is  in  the  hands  of  an  intelligent  mold-maker,  nor  how 
small  the  additional  expense.  It  is  important,  when  molds  are 
not  lined  with  galvanized  iron,  that  the  interior  be  not  merely 
surfaced,  but  that  exceeding  smoothness  and  protection  from 
warping  be  secured  by  repeatedly  alternating  sand-papering  with 
coats  of  shellac. 

In  a  thoroughly  equipped  factory  which  aims  to  supply  the 


82  CONCRETE-BLOCK  MANUFACTURE. 

demands  of  the  public  in  both  plain  and  ornamental  work,  a 
capable  modeler  is  a  valuable  employee.  In  one  factory  recently 
visited,  the  ability  of  the  modeler  and  mold-maker  were  of  so  high 
an  order  that  it  was  impossible  for  a  customer  to  suggest  any 
requirement  in  cement-work  which  could  not  be  properly  sup- 
plied without  recourse  to  outside  assistance.  That  is  the  ideal 
condition  which  will  be  approached  to  a  greater  or  less  degree, 
according  to  the  extent  of  the  manager's  appreciation  of  the 
importance  of  really  meeting  the  public  need. 

As  to  the  common  labor  employed  in  a  concrete-block  fac- 
tory, the  position  of  many  writers,  that  an  inferior  class  of  foreign 
labor  is  economical,  is  not  well  taken.  In  observing  the  opera- 
tion of  plants  in  which  the  major  portion  of  the  labor  is  intrusted 
to  the  hands  of  indifferent  and  incapable  workmen,  and  in  observ- 
ing the  operations  of  other  plants  in  which  the  laborers  are  keen, 
energetic,  and  careful,  and  in  inspecting  the  blocks  turned  out 
by  each  and  the  buildings  erected  therefrom,  note  has  been 
taken  of  the  ultimate  bankruptcy  of  the  one  and  of  the  increasing 
financial  success  of  the  other.  There  is,  perhaps,  no  class  of 
manufacturered  articles  in  which  the  personal  equation,  the 
integrity  and  knowledge  of  the  man  who  does  the  work,  is  more 
important  than  in  concrete  blocks;  and  it  is  impossible,  by  the 
purchase  of  the  best  and  most  expensive  machinery  or  by  the 
most  rigid  and  competent  superintendence,  to  eliminate  this 
factor. 

It  is  not  expedient  to  disregard  how  or  by  whom  the  blocks 
are  laid  in  the  wall.  The  best  blocks,  when  carelessly  laid,  pro- 
duce but  a  poor  and  ill-appearing  wall.  A  man  who  knew  block - 
construction  most  thoroughly  tersely  remarked,  in  inspecting 
an  especially  fine  wall,  "  Your  mason  knows  his  business." 
There  is  food  for  reflection  in  that  observation.  In  many  places 
the  brick-  and  stone-masons  appear  to  be  antagonistic  to  block- 


PLANT  EMPLOYEES.  83 

construction.  This  should  not  be,  and  the  condition  is  very 
often  caused  by  the  attitude  of  the  block-maker.  As  either 
brick-  or  stone-masons  can  satisfactorily  lay  the  blocks,  the  mat- 
ter should,  if  the  place  of  operation  be  unionized,  be  frankly 
submitted  to  the  trades  council  for  their  decision  as  to  who  shall 
lay  the  blocks.  Their  decision  should  be  accepted  by  all  parties 
concerned,  and,  if  that  decision  be  recognized  as  authoritative, 
harmony,  goodwill,  and  good  work  will  follow. 


CHAPTER  XVII. 

VOIDS. 

ELIMINATING  from  the  discussion  of  voids  considerations 
purely  technical,  it  may  be  said  that  voids  in  concrete  blocks 
are  the  result: 

1.  Of  improper  gradation  of  aggregate. 

2.  Of  careless  or  insufficient  mixing. 

3.  Of  inadequate  matrix. 

4.  Of  lack  of  proper  condensation. 

It  is  scarcely  necessary  to  state  that,  to  every  conscientious 
block-maker  and  to  every  proprietor  of  a  concrete-block  fac- 
tory who  desires  to  maintain  and  increase  his  patronage,  a  study 
of  the  causes  of  voids,  and  of  those  methods  by  which  they  may 
be  eliminated,  is  of  the  greatest  importance.  He  would  indeed 
be  a  novice  in  the  industry  who  failed  to  perceive  that  a  porous 
block  is  a  weak  block;  but  the  experienced  manufacturer  often 
makes  the  mistake  of  supposing  that  in  a  fine  aggregate  there 
is  less  porosity  than  in  a  coarse  one,  merely  because  the  individual 
voids  are  smaller,  and  hence  not  so  apparent  to  the  eye.  As  a 
matter  of  fact,  there  is  no  appreciable  difference  in  the  percentage 
of  voids  in  a  uniform  gravel  and  in  a  uniform  sand,  and  it  is  there- 
fore apparent  that  density  in  any  marked  degree  is  only  obtained 
by  such  relative  proportions  as  cause  the  larger  voids  in  the 
coarse  aggregate  to  become  filled  with  the  grains  of  the  smaller. 

84 


VOIDS.  85 

The  theory  of  correct  mixtures  and  the  methods  of  correct  pro- 
portioning have  received  treatment  in  the  chapter  devoted  to 
Proportioning,  and  it  is  necessary  to  add  only  that  an  observance 
of  the  methods  there  prescribed  will  be  found  the  most  facile 
means  for  the  elimination  of  voids. 

It  is  also  to  insufficient  mixing,  or  to  unintelligent  mixing, 
that  the  cause  of  porosity  may  often  be  traced.  Of  this  suffi- 
cient notice  is  taken  in  the  chapter  devoted  to  Mixing,  as  it  is 
evident,  upon  a  moment's  thought,  that  correct  manipulation 
alone  can  cause  the  finer  aggregate  to  assume  its  correct  position 
in  respect  to  the  coarser. 

The  adequacy  of  matrix,  or  the  use  of  a  sufficient  quantity 
of  cement  to  fill  the  voids  in  the  fine  aggregate,  is  not  only  one 
of  the  indispensable  means  of  producing  strength,  but  is  the 
most  potent  of  all  means  for  securing  impermeability,  inas- 
much as  it  is  the  cement  alone  which  can  so  thoroughly  seal  the 
pores  of  a  block  that  water  may  not  pass.  Too  much  attention 
has  been  given  to  means  for  reducing  the  amount  of  cement 
used  in  making  blocks.  Inasmuch  as  cement  is  the  most  expen- 
sive of  the  raw  materials,  and  hence  constitutes  a  considerable 
item  in  the  total  cost  of  production,  it  has  been  thought  advisable 
by  the  promoters  of  this  industry  to  adopt  every  means  for  its 
saving.  The  danger-line  has  too  often  been  passed.  It  is  not 
chiefly  cheapness,  but  more  especially  excellence,  which  will 
raise  the  concrete  block  to  an  important  place  among  building 
materials. 

On  every  hand  the  effect  of  improper  condensation  is  visible. 
Out  of  a  hundred  concrete  blocks  of  ordinary  manufacture, 
how  many  do  not  disclose,  on  close  and  careful  examination, 
an  unequal  degree  of  compactness  in  different  sections,  and 
how  many  are  free  from  pores  on  the  surface?  It  is  plain  that 
this  is  primarily  due  to  the  intermittence  of  energetic  and  languid 


86  CONCRETE-BLOCK  MANUFACTURE. 

tamping,  and  hence  we  have  as  remedies  the  pneumatic  tamper 
on  the  one  hand  and  the  mechanical  and  hydraulic  presses  on 
the  other.  While  the  hydraulic  press  makes  a  strong  point  of 
its  heavy  pressure,  it  would  seem  to  be  excessive,  as  it  is  evident 
that  there  is  a  limit  to  the  amount  of  pressure  which  can  be 
advantageously  employed.  If  the  particles  are  brought  close 
together  it  is  sufficient;  and  any  considerable  excess  of  pressure 
must  force  the  plastic  cement  from  between  the  particles  it  should 
bond,  or  cause  fracture  of  arched  aggregates.  It  would  seem 
that  the  rational  solution  of  condensation  is  reached  in  those 
presses  which  apply  a  reasonable  pressure. 


CHAPTER  XVIII. 

QUALITIES   OF   CONCRETE   BLOCKS. 

FIRST  in  importance  of  the  qualities  of  concrete  blocks  is 
that  freedom  from  cracks,  deformation,  and  disintegration  which 
cannot  be  better  denned  than  by  the  comprehensive  word  "  sound- 
ness." Whatever  be  the  other  qualities  of  a  block,  it  is  value- 
less without  soundness;  whatever  be  its  defects,  it  is  good  for 
something  if  sound.  It  is  scarcely  necessary  to  say  that  a  first 
requisite  of  a  sound  block  is  a  sound  cement.  Of  this  matter 
enough  has  been  said  in  the  chapter  on  Cement.  Of  the  quantity 
of  cement  it  may  be  added,  to  what  has  already  been  stated  in 
the  chapter  devoted  to  Proportioning  and  the  chapter  on  Voids, 
that  the  cement  must  thoroughly  coat  the  aggregate  in  order 
to  exercise  its  cementitious  or  bonding  function,  which  is  so 
essential  to  a  sound  concrete  block. 

The  matter  of  mixing  also  has  a  direct  action  upon  the  ulti- 
mate quality,  and  that  in  the  respect  last  mentioned. 

It  is  in  the  handling  and  curing  of  blocks  after  manufacture, 
however,  that  unsoundness  is  most  often  developed.  In  trans- 
ferring blocks  to  the  racks,  cars,  and  curing-yard,  latent  defects 
and  invisible  cracks  are  developed  which  ultimately  cause  the 
loss  of  the  entire  block,  or,  if  a  rigid  inspection  of  the  finished 
product  be  omitted,  may  result  in  failure  of  the  member  in  time 
of  need.  It  should  be  remembered  that  a  crack  in  a  freshly 

87 


88  CONCRETE-BLOCK  MANUFACTURE. 

made  block  never  heals,  but  rather  tends  to  extend  through 
the  block.  Hence  too  much  care  of  green  blocks  cannot  be 
exercised,  and  the  slightest  defect  should  cause  the  block  to  be 
immediately  returned  to  the  mixing-platform,  or,  if  the  cement 
has  already  set,  it  should  go  to  the  scrap-pile. 

In  curing,  lack  of  uniform  conditions  of  moisture  and  shade, 
as  well  as  air-drafts,  are  responsible  for  a  large  percentage  of 
both  surface  and  structural  cracks;  while  the  failure  to  properly 
dispose  blocks  for  curing,  allowing  them  to  rest  on  uneven  sur- 
faces, or  in  contact  with  one  another,  while  green,  permits  warp- 
ing and  results  in  twisted  blocks. 

In  general  it  may  be  said  that  soundness  results  from  those 
methods  of  manufacture  securing  perfect  homogeneity  of  mass, 
and  those  methods  of  curing  securing  uniform  treatment  to 
every  portion  of  the  block. 

Strength  is  the  quality  by  which  concrete  blocks  will  be  most 
usually  judged  in  making  comparisons  with  other  building  mate- 
rials. By  the  thorough  filling  of  voids,  already  so  strongly  recom- 
mended, great  compressive  strength  may  be  obtained,  while 
tensile  strength  approximating  the  capacity  of  neat  cement 
briquettes  may  be  attained  by  increasing  the  proportion  of  cement 
in  the  aggregate.  It  must,  however,  be  remembered  that  con- 
crete blocks,  like  all  other  materials,  have  their  obvious  uses 
and  their  fixed  limitations.  It  is  not  usually  necessary,  there- 
fore, to  give  great  thought  to  tensile  strength,  except  in  so  far 
as  concerns  the  resistance  to  lateral  stress  which  a  wall  is  designed 
to  withstand.  It  is  usual  to  make  provision  by  metal  reinforce- 
ment for  the  resistance  of  transverse  strain  and  the  distribu- 
tion of  concentrated  loads.  This  by  reason  of  the  greater  economy 
of  metal  in  tension  than  in  compression.  There  is  little  differ- 
ence in  the  compressive  and  tensile  strength  of  steel,  while  con- 
crete is  from  eight  to  ten  times  stronger  in  the  former  than  in 


QUALITIES  OF  CONCRETE  BLOCKS.  89 

the  latter.  It  is  therefore  plain  that  the  especial  function  of  the 
concrete  block  is  in  the  carrying  of  direct  vertical  loads. 

Of  course  no  concrete  will  exceed  the  strength  of  its  aggre- 
gate; but  if  proper  aggregate  be  used  in  relatively  correct  pro- 
portions, with  an  adequate  amount  of  cement  and  sufficient 
water  to  secure  thorough  crystallization,  if  the  manipulation  of 
the  mass  in  mixing  be  thorough  and  intelligent  and  the  block 
be  properly  condensed  and  properly  cured,  there  is  no  reason 
why  blocks  should  fail,  at  an  age  of  twenty-eight  days,  to  test 
from  2,000  to  3,000  pounds  per  square  inch  of  solid  surface,  i.e., 
making  no  allowance  for  the  hollow  space  in  the  wall.  The 
fact  that  individual  tests  have  been  made  as  high  as  2,600  pounds 
to  the  square  inch,  on  blocks  selected  from  lots  commercially 
made,  shows  the  practical  possibilities  of  good  work  on  correct 
lines.  The  fact  that  most  tests  reported,  upon  a  collection  of 
blocks  from  various  makers,  show  results  far  below  these  figures, 
indicates  either  that  many  processes  are  impractical  for  high- 
grade  work  or  that  many  operators  are  careless  and  incom- 
petent. 

Density  has  a  direct  relation  to  strength  and  an  indirect  rela- 
tion to  impermeability.  Density  refers  to  the  total  percentage 
of  solid  material  in  the  block,  being  opposed  to  porosity,  which 
is  the  total  percentage  of  voids.  While  mixing  and  condensa- 
tion are  quite  as  necessary  elements  in  the  securing  of  density 
as  in  the  attainment  of  other  desirable  qualities  of  concrete  blocks, 
it  is  especially  the  relation  of  proportioning  to  density  which 
requires  elucidation.  It  has  already  been  stated  that  a  fine 
aggregate  possesses  no  greater  density  than  a  coarse  one,  pro- 
viding each  be  of  the  same  uniformity  of  grain.  It  must  now 
be  observed  that  the  introduction  of  a  reasonable  quantity  of 
coarse  aggregate  into  the  fine  positively  increases  its  density. 
That  is  to  say,  if  into  a  quart  of  sand  one  introduces  a  pint  of 


9°  CONCRETE-BLOCK  MANUFACTURE. 

gravel,  the  density  is  increased  by  the  amount  of  voids  in  that 
amount  of  sand  replaced  by  the  solid  contents  of  the  gravel. 

Impermeability  is  an  essential  quality  in  a  good  concrete 
block.  The  means  of  securing  impermeability  are  so  closely 
interwoven  with  previous  observations  that  it  is  necessary  to 
say  only. that  it  rests  upon  the  use  of  an  adequate  proportion 
of  cement,  sufficiency  of  water,  thorough  mixing,  proper  gra- 
dation of  aggregate,  thorough  condensation,  and  careful  curing. 
Given  these  conditions  and  a  concrete  block  will  be  more  imper- 
meable than  the  average  of  other  building  materials.  The 
difference  between  density  and  impermeability  lies  in  the  fact 
that  the  latter  is  determined  by  the  size  and  continuity  of  voids 
rather  than  by  their  total  percentage.  It  is  therefore  evident 
that  a  fair  proportion  of  fine  sand  or  screenings  is  more  essential 
to  impermeability  than  to  density,  and  in  both  may  be  observed 
the  importance  of  the  rules  given  for  proportioning.  It  is  also 
well  to  remember  the  increased  impermeability  that  may  be 
secured  by  using  a  small  proportion  of  hydrated  lime.  Indeed, 
many  believe  that  herein  lies  the  most  practicable  method  of 
overcoming  permeability.  No  standard  building  material  is, 
of  itself,  waterproof  in  the  fullest  sense  of  that  much-abused  word. 
Neither  is  it  desirable  that  it  should  be  so,  as  the  result  would 
be  sweating  of  the  interior  due  to  failure  to  absorb  the  moisture 
developed  on  the  inner  surface.  It  has,  however,  been  the  desire 
of  block-makers  to  render  their  product  so  far  superior  to  brick 
in  this  respect  that  the  customary  furring  and  lathing  might 
be  eliminated,  and  the  cost  of  construction  reduced,  by  permitting 
the  application  of  plaster  directly  to  the  concrete  blocks.  It 
seems  that  the  only  means  so  far  adopted  insuring  absolute  and 
permanent  satisfaction  is  the  use  of  a  wall  so  constructed  that 
there  shall  be  a  continuous  horizontal  air-space,  precluding  the 
passage  of  moisture,,  between  the  outer  and  inner  face.  It  is,  of 


QUALITIES  OF  CONCRETE  BLOCKS.  91 

course,  true  that  many  preparations  are  offered,  both  as  ingre- 
dients in  the  mixture  and  as  washes  to  be  used  on  the  exterior 
after  completion  of  construction;  but  there  are  serious  questions 
yet  undecided  as  to  the  deleterious  action  of  the  former  and 
the  permanence  of  the  latter. 

The  fire-resisting  quality  of  concrete  blocks  is,  month  by 
month,  becoming  more  marked  and  more  thoroughly  recog- 
nized. In  the  early  days  of  the  use  of  concrete  for  the  construc- 
tion of  buildings,  little  thought  was  given  to  its  power  as  a  fire- 
resistant;  and  it  was  generally  assumed  that,  being  a  hydrated 
product,  it  would  disintegrate  at  a  lower  temperature  than  the 
clay  products,  in  which  excessive  heat  created  no  chemical  action. 
It  was,  of  course,  known  that  building-stones  would  spall  under 
the  extremes  of  heat  and  the  copious  application  of  water,  and 
that  the  shell  or  matrix,  which  in  really  well-made  concrete 
protected  the  aggregate,  greatly  reduced  the  tendency  to  disinte- 
grate. It  was  not,  however,  until  the  Baltimore  fire  left  ruins  of 
concrete  structures  in  condition  far  superior  to  other  so-called 
fireproof  construction  that  the  attention  of  insurance  experts 
was  seriously  centered  upon  concrete  as  the  fireproof  building 
material  of  the  future.  It  was  then  found  by  exhaustive  experi- 
ments and  observations  that  concrete  did  not  give  off  its  water 
of  chemical  composition  so  readily  as  had  been  supposed,  but 
that  an  approximate  temperature  of  1000°  Fahrenheit  was  neces- 
sary to  dehydrate  the  outer  quarter  inch,  and  this  quarter  inch, 
so  dehydrated,  became  non-conductive,  making  it  still  more 
difficult  to  dehydrate  the  interior  which  it  protected.  It  is  true 
that  examples  of  concrete-block  buildings  which  have  withstood 
actual  fires  are  somewhat  meager.  Fig.  22  shows  a  building 
which  withstood  a  fire  at  Carbon,  Indiana,  and  from  the  illustra- 
tion it  will  be  noted  how  complete  was  the  surrounding  devas- 
tation. Fig.  23  shows  a  building  which  similarly  withstood  a 


CONCRETE-BLOCK  MANUFACTURE. 


conflagration  at  Estherville,  Iowa.     Concerning  the  former  it  is 
stated  that  no  damage  was  done  except  the  breakage  of  window- 


K 


glass  by  the  intense  heat.  Concerning  the  latter  it  is  reported 
that,  while  the  fiercest  flames  from  a  large  adjoining  building 
were  attacking  the  outside,  the  inner  side  of  the  wall  was  so 


UNIVERSITY 

OF 

£iL/roRN\^ 


BLOCKS. 


93 


slightly  heated  that  the  hand  could  be  held  against  it.  It  must 
not  be  forgotten  that,  while  it  is  the  quality  of  concrete  itself 
which  prevents  its  destruction  by  fire,  it  is  due  to  the  interior 
air-space  of  the  wall  that  the  heat  is  not  transmitted  to  the  interior 
being  but  a  special  application  of  the  same  principle  which  makes 
a  concrete-block  house  warm  in  winter  and  cool  in  summer.  It 
must  also  be  remembered  that  the  greater  the  air-space,  and 


FIG.  23. — Ruins  of  Estherville  Fire. 

the  more  nearly  continuous  it  be,  the  less  will  be  the  heat  con- 
ductivity of  the  wall. 

While  vast  sums  are  annually  expended  to  secure,  in  the 
better  class  of  buildings,  some  freedom  from  transmission  of 
sound,  this  desirable  result  is  obtained  with  no  additional  expense, 
but  becomes  merely  an  incidental  matter,  by  the  use  of  con- 
crete-block walls. 


94  CONCRETE-BLOCK  MANUFACTURE. 

It  is  likewise  incident  to  this  class  of  construction  that  ver- 
min find  no  harbor  in  its  walls.  Indeed,  the  general  sanitary 
conditions  of  concrete-block  construction  are  so  much  a  matter 
of  course  that  their  real  excellence  is  scarcely  appreciated. 

There  is  no  other  class  of  construction  in  use  at  the  present 
day  which  offers  such  marked  capacity  for  scientific  ventilation 
by  properly  located  interior  and  exterior  ventilators  communi- 
cating through  the  hollow  spaces  of  the  wall,  but  overcoming 
the  harshness  of  a  direct  draft  of  air. 

Of  the  durability  of  concrete  blocks  much  may  be  said  and 
little  may  be  necessary.  It  is  known  to  readers  of  this  book 
that  concrete  buildings  have  stood  in  perfect  condition  in  vari- 
ous European  countries  for  hundreds  of  years,  while  the  ruins 
of  ancient  cities  show  many  evidences  of  concrete  work  in  a 
good  state  of  preservation  after  thousands  of  years.  The  reader 
may  well  ask  if  the  concrete  blocks  of  to-day  are  made  with  the 
same  care,  and  if  they  will  possess  the  same  degree  of  durability. 
Answer  may  be  made  in  the  affirmative  for  some,  and  must  needs 
be  in  the  negative  for  others.  The  industry  is,  however,  capable 
of  elevation  to  that  high  standard  where  an  affirmative  answer 
may  soon  be  applicable  to  all;  and  it  is  the  chief  purpose  of  this 
treatise  to  influence  some  block-makers  toward  that  intelligent 
and  careful  manufacture  which  shall  eventually  bring  this  great 
industry  in  its  entirety  to  that  high  plane. 


CHAPJER  XIX. 

TESTING     BLOCKS. 

IT  is  a  curious  fact  that  most  operators  of  concrete-block 
plants  utterly  neglect  the  matter  of  testing  their  product.  It 
does  not  appear  that  their  negligence  is  caused  by  any  lack  of 
faith  in  the  quality  of  the  blocks,  or  in  their  ability  to  withstand 
the  tests,  but  merely  because  the  lack  of  technical  training  has 
not  impressed  the  average  concrete-block  maker  with  the  value 
of  proper  tests.  He  hears  of  cement-testing,  and  glances  at  the 
results  of  tests  made  upon  the  particular  brand  of  cement  he  is 
using — and  stops  there.  He  fails  to  recognize  that  every  part 
of  the  process  of  making  blocks,  from  the  time  the  raw  materials 
reach  his  yard  until  the  finished  blocks  are  in  the  wall,  as  well 
as  every  shovelful  of  material  in  the  blocks,  has  a  definite  rela- 
tion to  the  tests  which  the  blocks  will  pass.  He  fails  to  recog- 
nize the  fact  that  his  processes  may  be  immeasurably  improved 
by  tests  which  will  warn  him  as  to  wherein  lies  his  weakness.  If, 
on  the  other  hand,  he  is  sure  he  has  no  weakness,  tests  will  show 
to  the  public,  whose  trade  he  solicits,  how  far  the  material  he 
offers  excels  competing  building  materials.  It  is  of  especial 
advantage  to  the  man  who  is  making  thoroughly  good  blocks 
to  have  properly  certified  tests  of  his  product  in  comparison 
with  all  other  building  materials  in  common  use  in  his  locality. 

The  exhaustive  researches  made  in  connection  with  the 
testing-laboratories  of  the  city  of  Philadelphia  have  resulted 

95 


96  CONCRETE-BLOCK  MANUFACTURE. 

in  specifications  of  such  excellence  for  the  testing  of  concrete 
blocks  that  the  reader  cannot  be  better  advised  as  to  complete 
tests  than  by  a  careful  study  of  sections  three  to  fourteen,  in- 
clusive, of  the  "  Specifications  Governing  the  Method  of  Testing 
Hollow  Concrete  Blocks  used  under  the  Supervision  of  the 
Bureau  of  Building  Inspection  of  the  city  of  Philadelphia." 
They  are  as  follows: 

3.  The  material  must  be  subjected  to  the  following  tests: 
Transverse,  Compression,  Absorption,  Freezing,  and  Fire.     Addi- 
tional tests  may  be  called  for  when,  in  the  judgment  of  the  Chief 
of  the  Bureau  of  Building  Inspection,  the  same  may  be  necessary. 
All  such  tests  must  be  made  in  some  laboratory  of  recognized 
standing,  under  the  supervision  of  the  engineer  of  the  Bureau 
of  Building  Inspection.     The  tests  will  be  made  at  the  expense 
of  the  applicant. 

4.  The  results  of  the  tests,  whether  satisfactory  or  not,  must 
be  placed  on  file  in  the  Bureau  of  Building  Inspection.     They 
shall  be  open  to  inspection  upon  application  to  the  Chief  of  the 
Bureau,  but  need  not  necessarily  be  published. 

5.  For  the  purpose  of  tests,  at  least  twenty  (20)  samples  or 
test-pieces   must    be    provided.     Such    samples   must   represent 
the  ordinary  commercial  product.     They  may  be  selected  from 
stock  by  the  Chief  of  the  Bureau  of  Building  Inspection,  or  his 
representative,  or  may  be  made  in  his  presence  at  his  discretion. 
The  samples  must  be  of  the  regular  size  and  shape  used  in  con- 
struction.    In  cases  where  the  material  is  made  and  used  in 
special  shapes  and  forms  too  large  for  testing  in  the  ordinary 
machines,   smaller-sized    specimens    shall  be  used,   as    may  be 
directed  by  the  Chief  of  the  Bureau  of  Building  Inspection,  to 
determine  the  physical  characteristics  specified  in   Section  3. 

6.  The  samples  may  be  tested  as  soon  as  desired  by  the  appli- 
cant, but  in  no  case  later  than  sixty  days  after  manufacture. 


TESTING  BLOCKS.  97 

7.  The  weight  per  cubic  foot  of  the  material  must  be  de- 
termined. 

8.  Tests  shall  be  made  in  series  of  at  least  five,  except  that 
in  the  fire-tests  a  series  of  two  (four  samples)  are  sufficient.     Trans- 
verse tests  shall  be  made  on  full-sized  samples.     Half  samples 
may  be  used  for  the  crushing,  freezing,   and  fire  tests.     The 
remaining  samples  are  kept  in  reserve,  in  case  unusual  flaws  or 
exceptional  or  abnormal  conditions  make  it  necessary  to  dis- 
card certain  of  the  tests.     All  samples  must  be  marked  for  iden- 
tification and  comparison. 

9.  The  transverse  test  shall  be  made  as  follows:   The  sample 
shall  be   placed   flatwise  on   two  rounded  knife-edge  bearings 
set  parallel,  seven  inches  apart.     A  load  is  then  applied  on  top, 
midway  between  the  supports,  and  transmitted  through  a  similar 
rounded  knife-edge,  until  the  sample  is  ruptured.     The  modulus 
of  rupture  shall  then  be  determined  by  multiplying  the  total  break- 
ing load  in  pounds  by  twenty-one  (three  times  the  distance  between 
supports  in  inches),  and  then  dividing  the  result  thus  obtained 
by  twice  the  product  of  the  width  in  inches  by  the  square  of 
the  depth  in  inches.     No  allowance  shall  be  made  in  figuring 
the  modulus  of  rupture  for  the  hollow  spaces. 

10.  The  compression  test  shall  be  made  as  follows:   Samples 
must  be  cut  from  blocks  so  as  to  contain  a  full-web  section.     The 
sample  must  be  carefully  measured,  then  bedded  flatwise  in  plaster 
of  Paris  to  secure  a  uniform  bearing  in  the  testing-machine  and 
crushed.     The  total  breaking-load  is  then  divided  by  the  area 
in   compression   in    square  inches;    no   deduction   to   be   made 
for  hollow  spaces;    the  area  will  be  considered  as  the  product 
of  the  width  by  the  length. 

1 1 .  The  absorption- test  shall  be  made  as  follows :  The  sample 
is  first  thoroughly  dried  to  a  constant  weight.     The  weight  must 
be  carefully  recorded.     It  is  then  placed  in  a  pan  or  tray  of  water, 


gS  CONCRETE-BLOCK  MANUFACTURE. 

face  downward,  immersing  it  to  a  depth  of  not  more  than  one- 
half  inch.  It  is  again  carefully  weighed  at  the  following  periods: 
Thirty  minutes,  four  hours,  and  forty-eight  hours,  respectively, 
from  the  time  of  immersion,  being  replaced  in  the  water  in  each 
case  as  soon  as  the  weight  is  taken.  Its  compressive  strength , 
while  still  wet,  is  then  determined  at  the  end  of  the  forty-eight- 
hour  period,  in  the  manner  specified  in  Section  10. 

12.  The  freezing-tests    are  made  as  follows:    The  sample  is 
immersed,  as  described  in  Section  n,  for  at  least  four  houis 
and  then  weighed.     It  is  then  placed  in  a  feezing-mixture  or  a 
refrigerator,  or  otherwise  subjected  to  a  temperature  of  less  than 
15  degrees  F.  for  at  least  twelve  hours.     It  is  then  removed  and 
placed  in  water,  where  it  must  remain  for  at  least  one  hour,  the 
temperature  of  which  is  at  least  150  degrees  F.     This  operation 
is  repeated  ten  (10)  times,  after  which  the  sample  is  again  weighed, 
while  still  wet  from  the  last  thawing.     Its  crushing  strength  should 
then  be  determined  as  called  for  in  Section  10. 

13.  The  fire- test  must  be  made    as  follows:    Two  samples 
are  placed  in  a  cold  furnace  in  which  the  temperature  is  gradu- 
ally raised  to  1700   degrees  F.,  and  the  test-piece  must  be  sub- 
jected to  this  temperature  for  at  least  thirty  minutes.     One  of  the 
samples  is  then  plunged  in  cold  water  (about  50  degrees  to  60 
degrees  F.)  and  the  results  noted.     The  second  sample  is  per- 
mitted to  cool  gradually  in  air  and  the  results  noted. 

14.  The  following  requirements  must  be  met  to  secure  an 
acceptance  of  materials.     The  modulus  of  rupture  for  concrete 
blocks  at  twenty- eight  days  old  must  average  one  hundred  and  fifty, 
and  must  not  fall  below  one  hundred  in  any  case.     The  ultimate 
compressive  strength  at  twenty-eight  days  must  average  one  thou- 
sand pounds  per  square  inch,  and  must  not  fall  below  seven  hun- 
dred in  any  case.     The  percentage  of  absorption  (being  the  weight 
of  water  absorbed  divided  by  the  weight  of  the  dry  sample)  must 


TESTING  BLOCKS. 


99 


not  average  higher  than  15%,  and  must  not  exceed  20%  in  any 
case.  The  reduction  of  compressive  strength  must  not  be  more 
than  thirty- three  and  one- third  per  cent.,  except  that,  when  the 
lower  figure  is  still  above  one  thousand  pounds  per  square  inch, 


WHAT 


not 


FIG.  24. — Column   Demonstrating   Compressive   and  Lateral   Strength. 

the  loss  in  strength  may  be  neglected.  The  freezing  and  thawing 
process  must  not  cause  a  loss  in  weight  greater  than  ten  per  cent., 
nor  a  loss  in  strength  of  more  than  thirty-three  and  one-third 
per  cent.,  except  that,  when  the  lower  figure  is  still  above  one  thou- 


ioo  CONCRETE-BLOCK  MANUFACTURE. 

sand  pounds  per  square  inch,  the  loss  in  strength  may  be  neg- 
lected.    The  fire-test  must  not  cause  the  material  to  disintegrate. 


It  is  the  practice  of  very  many  manufacturers  to  erect  per- 
manent exhibits  of  concrete  blocks  in  which  a  practical  test  of 
one  or  more  of  the  essential  qualities  of  good  blocks  is  embodied. 
To  many  these  tests  are  more  convincing  than  are  the  certified 
laboratory  tests,  because  of  their  unfamiliarity  with  the  methods 
of  conducting  the  latter,  and  their  habit  of  believing  only  in 
that  which  they  see.  In  Fig.  24  is  presented  a  very  interesting 
demonstration  of  the  resistance  of  a  perfectly  bonded  wall  to 
lateral  strain,  as  well  as  the  capability  of  concrete  blocks  to  sup- 
port heavy  loads.  This  column,  which  was  erected  by  a  St 
Louis  operator,  is  six  feet  square  and  twenty  feet  high,  having 
an  interior  area  of  sixteen  square  feet.  The  column  is  loaded 
with  dry  sand.  The  total  weight  of  one  hundred  thousand 
pounds  is  carried  by  eight  feet  of  12"  wall,  50%  hollow. 


CHAPTER  XX. 

BLOCK  USES. 

THE  illustrations  used  in  connection  with  this  chapter  are 
sufficient  evidence  of  the  adaptability  of  concrete  blocks  to  all 


FIG.  25. — Methodist  Church,  McCook,  Nebraska. 

classes  of  building  construction,  and  of  their  satisfactory  employ- 
ment in  completed  structures  of  various  kinds  and  sizes  through- 
out the  United  States. 


101 


102  CONCRETE-BLOCK  MANUFACTURE. 


FIG.  26. — Entrance  to  Cottage  Hill  Cemetery,  Brazil,  Indiana. 


FIG.  27. — Cottage,  Nashville,  Tennessee. 


OF  THE 

UNIVERSITY 

OF 


BLOCK  USES.  105 

Figs.  26  and  35  show  entrance  gates.  Figs.  25  and  28  give 
views  of  churches.  Figs.  27,  29  to  32,  and  34  illustrate  some 
of  the  various  designs  in  residences.  In  Fig.  33  is  shown  an 
office-building,  and  in  Fig.  36  a  state  institution. 

This  list  might  easily  be  multiplied,  but  the  illustrations 
presented  have  been  selected  from  a  large  collection  as  suffi- 
ciently emphasizing  the  capacity  of  the  concrete  block  for  any 
style  of  structure.  For  dwelling-houses  there  can  be  no  build- 
ing material  at  any  price  which  will  afford  so  great  ultimate  sat- 
isfaction. The  introduction  of  a  fireproof  material  in  the  con- 
struction of  dwellings  of  moderate  size  is  an  innovation,  and 
the  departure  from  the  time-honored  fire-trap  construction  for 
the  homes  of  the  great  masses  of  the  people  is  welcomed  on  all 
sides. 

Perhaps  the  reader  will  pardon  a  moment's  digression,  and 
consider  what  it  means  to  the  average  well-to-do  American  farmer 
of  to-day,  isolated  from  the  fire  protection  of  our  cities,  to  have 
a  building  material  which  protects  him  from  that  enemy  which 
he  most  fears.  How  long  a  step  it  is  from  the  frame-houses 
with  which  the  countryside  is  dotted,  and  which  are  a  constant 
menace  to  the  lives  and  property  of  the  occupants,  to  concrete- 
block  construction,  which  presents  the  greatest  fire-resisting  quali- 
ties, and  which  may  be  secured  at  but  slightly  increased  initial 
cost,  while  the  subsequent  freedom  from  paint  and  repairs  makes 
the  ultimate  expenditure  less  than  for  wooden  buildings!  Simi- 
lar construction,  but  of  plainer  and  less  expensive  type,  is  adapted 
to  barns  and  all  accessory  buildings. 

To  those  who  dwell  in  cities,  the  fireproof  quality  of  concrete 
blocks  appeals  quite  as  strongly,  since  reliance,  in  fierce  con- 
flagrations, must  at  last  rest  upon  the  integrity  of  the  individual 
building. 

In  the  construction  of  buildings  intended  to  house  stocks  of 


io6 


CONCRETE-BLOCK  MANUFACTURE. 


merchandise,  the  argument  applies  with  even  stronger  financial 
force.  If,  as  is  often  the  case  in  smaller  establishments,  the 
store  be  left  without  a  watchman  at  night,  one's  all  may  be  at 
the  mercy  of  the  power  of  the  building  to  resist  the  flames.  How 
small  the  protection  afforded  the  merchant  by  the  average 
building  occupied  for  mercantile  purposes! 


FIG.  29. — Residence,  Nashville,  Tennessee. 

Sight  must  not  be  lost  of  those  other  superior  qualities  which 
make  block  construction  so  eminently  useful.  The  lightness 
of  walls  in  proportion  to  the  load  they  will  carry  with  a  satisfac- 
tory factor  of  safety;  the  low  degree  of  heat  conductivity  which 
renders  a  home,  a  church,  or  a  public  building  comfortable  dur- 
ing the  heated  term  and  saves  25%  of  the  winter's  fuel  bill;  the 
protection  from  transmission  of  sound,  which  will  be  appreciated 
by  careful  builders;  the  facility  with  which  pipes  and  wires 


or  THE 
UNIVERSITY 

£&LIF< 


BLOCK  USES. 


in 


FIG.  32. — Residence  at  Denver,  Colorado. 


FIG.  33. — Warburton  Building,  Tacoma,  Washington. 


112 


CONCRETE-BLOCK  MANUFACTURE. 


may  be  laid  in  the  hollow  walls,  and  the  ease  with  which  they 
may  be  reached  for  repair  if  suitably  disposed  openings  be  arranged 
when  building,  with  covers  quickly  removable  in  case  of  necessity; 


the  freedom  from  moisture,  which  appeals  alike  to  one  who 
seeks  comfort  or  health  and  to  one  who  seeks  economy  by  elim- 
ination of  furring  and  lathing;  the  adaptability  of  blocks  to  any 


OF  THE   . 

UNIVERSITY 

OF 


BLOCK  USES.  115 

shape  or  size,  which  secures  the  builder's  good  will;  the  appear- 
ance of  really  good  blocks  and  the  readiness  with  which  they 
yield  to  artistic  decorative  features,  which  are  sources  of  delight 
to  the  architect, — all  these,  and  more,  are  the  reasons  which 
account  for  the  adoption  of  concrete  blocks  in  the  buildings 


FIG.  36. — Nebraska  State  Normal  School,  Kearney,  Nebraska. 

illustrated,  and  in  a  very  great  number  of  other  important  build- 
ings of  various  uses  and  diversified  architecture. 

In  closing  this  chapter,  it  is  desired  to  especially  direct  the 
reader's  attention  to  the  Nebraska  State  Normal  School  Build- 
ing shown  in  Fig.  36,  for  the  reason  that  it  demonstrates  the  injus- 
tice of  the  oft-repeated  criticism  of  certain  architects  that  con- 
crete blocks  cannot  be  made  to  fit  their  plans.  The  plans  for 
this  structure  were  made  in  contemplation  of  using  cut  stone, 


n6  CONCRETE-BLOCK  MANUFACTURE. 

and  the  specifications  provided  for  various  widths  of  courses  and 
fractional  sizes  most  unusual  in  block  construction.  Those  in 
charge  of  the  work  were  quick  to  recognize  the  great  opportunity 
here  afforded  the  concrete-block  industry  to  demonstrate  its 
adaptability,  and  they  complied  with  the  specifications  as  drawn. 


CHAPTER  XXI. 

CAUSES   OF   FAILURE. 

IN  considering  those  causes  which  have  in  some  cases  led  to 
failure  in  the  manufacture  of  concrete  blocks,  and  in  other  cases 
have  prevented  their  successful  introduction  in  certain  locali- 
ties, it  is  well  to  distinguish  between  the  errors  of  the  machine- 
manufacturer  and  those  of  the  block-maker.  For  convenience 
the  latter  will,  in  this  chapter,  be  designated  as  the  operator  and 
the  former  as  tpe  manufacturer. 

The'most  culpable  error  of  the  manufacturer  lies  in  his  failure 
to  recognize  the  merits  of  competing  machines,  in  his  real  or 
assumed  ignorance  of  the  points  of  superiority  which  have  been 
devised  by  another,  and  in  his  persistent  refusal  to  accept  cer- 
tain modifications  in  devices  or  process  which  will  enable  the 
operator  of  his  machine  to  more  fully  meet  the  public  demand. 
It  would  be  well  for  the  manufacturer  to  realize  that  the  public 
will  not  with  patience  accept  what  he  may  choose  to  give,  but 
that  the  public  will  have  what  it  desires,  and^tfhat  the  require- 
ments of  good  construction  demand.  If  hfe  do  not  anticipate 
that  demand,  and  if  he  be  not  prepared  to-iaeet  it,  the  public 
will  go  elsewhere,  and,  still  failing  to  find  what  is  sought,  will 
devise  ways  and  means  on  its  own  behalf,  without  considering 
the  manufacturer  individually  or  collectively. 

Nowhere  is  this  absence  of  consideration  for  the  public  good 

more  apparent  than  in  the  failure  of  manufacturers  to  provide 

117 


Ii8  CONCRETE-BLOCK  MANUFACTURE. 

a  uniform  standard  of  sizes  for  concrete  blocks.  There  are  but 
few  machines  which  individually  offer  all  that  is  needed  in 
the  construction  of  buildings,  and  hence,  as  stated  in  a  former 
chapter,  a  good  mold-maker  is  a  requisite  of  a  successful  factory. 
The  adherence  of  each  manufacturer  to  an  arbitrary  size  of 
block  seems  to  have  no  better  motive  than  the  prevention  of  the 
joint  use  of  his  own  machine  and  that  of  a  competitor,  each  of 
which  might  supply  those  blocks  most  advantageously  made 
on  the  respective  machines.  Certainly  for  this  diversity  and 
consequent  annoyance  to  the  public  there  is  no  reason  and  no 
excuse.  If  the  concrete- block  industry  shall  ever  attain  that 
universal  introduction  to  which  the  inherent  qualities  of  well- 
made  concrete  justly  entitle  it,  and  to  which  the  added  qualities 
peculiar  to  hollow  concrete  walls  add  mighty  emphasis,  the  manu- 
facturers must  become  imbued  with  somewhat  of  that  spirit  of 
co-operation  which,  in  these  latter  days,  is  recognized  as  a  prime 
factor  in  the  development  of  every  great  industry,  and  which 
has  been  by  no  means  the  least  of  those  causes  which  have  brought 
success  to  every  great  enterprise  of  our  time. 

Scarcely  less  worthy  of  attention  is  the  careless  treatment 
which  operators  continually  receive  at  the  hands  of  those  whose 
machines  they  purchase,  and  whose  interests  should  be,  and  unal- 
terably are,  thereafter  allied  with  their  own.  It  should  be  the 
first  consideration  of  the  manufacturer  to  place  machines  in 
the  hands  of  those,  and  those  only,  whose  capital  and  knowl- 
edge are  adequate  to  insure  success;  and  it  should  be  the  second 
consideration  to  give  the  operator  such  full  and  complete  instruc- 
tion and  information  as  will  fairly  aid  him  to  attain  ultimate 
success.  It  is  perhaps  unfair  to  place  all  of  this  blame  on  the 
manufacturer  when  so  much  of  it  is  in  reality  chargeable  to  his 
salesmen  in  the  field.  It  is  impossible  to  consider  this  phase 
of  the  question  without  bringing  up  the  old  contention  of  the 


CAUSES  OF  FAILURE.  119 

commission  salesman  versus  the  salary  salesman,  as  it  is  evi- 
dent that  self-interest  will  not  permit  the  former  to  lose  a  sale 
to  any  one  who  is  willing  to  buy,  even  though  he  may  know  that 
it  is  not  for  the  ultimate  good  of  the  vendor  or  the  vendee;  nor 
can  he  be  expected  to  spend  his  time,  after  consummation  of  a  sale, 
in  giving  those  instructions  which  are  so  helpful.  The  practice 
of  men  in  the  field  on  commission  is  to  know  barely  enough  of 
the  business  to  enable  them  tp  effect  sales.  The  practice  of  a 
salaried  man  is  to  know  the  business  from  alpha  to  omega,  and 
to  dispense  that  knowledge  for  the  good  of  his  house  in  con- 
nection with  past,  present,  and  future  sales.  To  briefly  sum- 
marize, it  may  be  said  that  manufacturers  should  avoid  a  short- 
sighted policy,  and  should  endeavor  to  take  advantage  of  every 
opportunity  to  raise  the  quality  of  the  work  produced  by  their 
machines. 

Considering  the  causes  of  failure  properly  chargeable  to  the 
operator,  the  most  apparent  may  be  said  to  be  lack  of  knowl- 
edge of  the  nature  and  action  of  Portland  cement.  The  man 
who  buys  a  machine  is,  in  very  many  instances,  ignorant  of 
cement  beyond  the  meager  and  sometimes  inaccurate  statements 
of  machine  catalogues.  It  is  his  first  duty  to  study  cement 
theoretically  and  practically  until  he  really  knows  it.  The 
operators  who  have  done  this  have  been  uniformly  successful. 
Another  cause  of  failure  is  reliance  on  cement  alone,  and  con- 
sequent neglect  as  to  character  and  proportioning  of  aggregate. 
The  fixed  proportions  usually  mentioned  in  manufacturers'  cata- 
logues are  based  merely  on  average  conditions,  and  may  or  may 
not  be  applicable  to  local  materials.  The  use  of  unequal  per- 
centages of  water  is  a  fruitful  source  of  failure,  as  making  one 
batch  wetter  than  another  means  a  variation  not  only  in  strength 
and  density  but  in  color  as  well.  The  proportion  of  water  will 
not  be  the  same  with  different  aggregates,  and  should  therefore 


120  CONCRETE-BLOCK  MANUFACTURE. 

be  determined  in  respect  to  local  materials,  but,  when  once  deter- 
mined, should  be  closely  adhered  to  by  a  system  of  accurate 
measuring.  Careless  curing  has  caused  a  very  large  number 
of  failures,  and  it  is  hoped  the  operator  will  give  careful  heed 
to  the  chapter  devoted  to  that  subject.  Perhaps  it  is  the  inor- 
dinate desire  for  cheapness  rather  than  quality  which  has  led 
many  block-makers  astray.  The  constant  effort  should  be  to 
excel  in  quality,  and  to  keep  the  cost  at  the  lowest  possible  figure 
consistent  with  high-class  work.  This  is  merely  a  matter  of 
business  management  and  factory  superintendence,  and  the 
reduction  in  cost  should  never  encroach  upon  the  real  good- 
ness of  the  product.  Careless  laying  has  prejudiced  builders 
against  the  use  of  blocks  otherwise  satisfactory,  and  of  this  a 
previous  chapter  has  dealt  in  detail. 

Perhaps  one  of  the  greatest  disadvantages  of  concrete  blocks 
is  their  ready  adaptability  to  any  design  or  decorative  feature. 
In  the  hands  of  the  skillful  and  artistic  builder,  the  merits  of  this 
adaptability  are  invaluable.  In  the  hands  of  the  unskilled  and 
inartistic,  the  same  adaptability  becomes  valueless,  and  results 
in  such  hybrid  designs  and  grotesque  architecture  as  to  disgust 
those  who  appreciate  correct  lines  in  building.  The  operator 
must  realize  that  the  vast  possibilities  of  concrete-block  con- 
struction must  not  be  abused,  but  that  their  use  must  be  directed 
by  those  whose  natural  artistic  tastes  and  architectural  training 
fit  them  to  so  dispose  the  various  decorative  features  that  a  sym- 
metrical and  pleasing  structure  may  result. 


CHAPTER  XXII. 

s 

COST. 

IN  any  computation  of  cost  in  connection  with  the  manufac- 
,  ture   of   concrete  blocks,  certain   factors   require   consideration 

which  can  only  be  determined  by  an  exact  knowledge  of  local 
conditions.  Hence  the  customary  practice  of  assuming  an 
arbitrary  standard  of  prices  becomes  misleading  for  more  rea- 
sons than  are  apparent  to  the  casual  reader.  This  is  but  one 
instance  of  the  many  mistakes  which  have  been  made  in  the 
promotion  of  this  industry  by  continued  effort  to  avoid  scientific 
and  technical  methods.  It  will  be  found  in  actual  practice  that 
the  factors  which  must  be  determined  before  any  reliable  cost 
calculation  can  be  made  are  as  follows: 

1.  Cost  of  cement. 

2.  Cost  of  sand  or  screenings. 

3.  Cost  of  gravel  or  broken  stone. 

4.  Relative  proportions  of  fine  and  coarse  aggregate. 

5.  Exact  proportion  of  cement. 

6.  Relation  between  volume  of  aggregate   and  volume 

of  compact  concrete. 

7.  Average  rate  of  actual  production  per  capita  per  day. 

8.  Price  of  different  grades  of  labor  per  day. 

9.  Cost  of  hauling  finished  product. 

121 


122  CONCRETE-BLOCK  MANUFACTURE. 

10.  Cost  of  administration: 

a.  Superintendence. 

b.  Advertising. 

c.  Office  expense. 

11.  Incidentals: 

d.  Depreciation  of  plant. 

e.  Repair  allowance. 

/.   Interest  on  investment. 

g.  Periodicals,  literature,  and  conventions. 

Those  who  contemplate  engaging  in  the  manufacture  of  con- 
crete blocks  will  view  the  foregoing  lightly,  and  ask  of  what  use 
is  so  careful  an  analysis.  Those  who  have  succeeded  will  recog- 
nize the  foundation  on  which  they  have  builded.  Those  who 
have  failed  will  frankly  admit  that  a  careful  study  of  this  analysis 
had  saved  them  loss. 

Inasmuch  as  the  net  weight  of  Portland  cement  is  94  Ibs. 
per  bag,  and  the  average  weight  per  cubic  foot  of  loose  Portland 
cement  is  92  Ibs.,  it  will  be  sufficiently  accurate  to  consider  the 
contents  of  a  bag  as  one  cubic  foot,  and  this  method  will  greatly 
simplify  cost  computation,  inasmuch  as  sand  and  gravel  are 
customarily  valued  by  the  cubic  yard.  The  cost  of  fine  and 
coarse  aggregate  must  be  separately  ascertained;  and  the  pro- 
portions in  which  they  are  to  be  mixed  must  be  determined,  as 
well  as  the  exact  proportion  of  cement  to  be  incorporated.  It 
must  be  observed  that  at  every  step  of  the  process  it  is  essential 
that  local  conditions  govern.  A  variation  in  the  aggregate,  such 
as  the  introduction  of  coarser  material,  will  often  effect  a  mate- 
rial reduction  in  the  necessary  amount  of  cement,  and  result  in 
cost-saving. 

We  now  approach  the  most  intricate  part  of  the  computa- 
tion. It  is  usual  for  block-makers  to  consider  that  one  cubic 
foot  of  gravel  and  a  half  cubic  foot  of  sand  will  have  a  volume 


COST.  123 

of  ij  cu.  ft.  when  thoroughly  mixed.  It  is  a  fact  that  a  con- 
siderable portion  of  the  sand  enters  the  voids  of  the  gravel  and 
decreases  the  volume.  The  same  is,  of  course,  true  of  cement 
and  sand.  It  is  therefore  evident  that,  owing  to  variation  in 
local  size,  shape,  and  gradation  of  aggregate,  the  actual  amount 
required  to  make  a  certain  volume  of  mixed  aggregate  can  only 
be  determined  by  actual  trial.  The  different  materials  locally 
available  will  require  different  percentages  of  water,  broken 
stone  usually  taking  more  than  gravel.  Again,  different  sands 
will  show  different  variations  in  volume  for  the  same  percentage 
of  moisture.  Therefore  the  volume  of  wet  concrete  obtainable 
from  dry-mixed  concrete  can  be  known  only  from  actual  experi- 
ment. The  different  processes  of  manufacturing  blocks,  as 
well  as  the  different  materials  used,  involve  varying  percentages 
of  reduction  in  volume  by  compression  in  molding.  This,  like 
the  previous  percentages,  must  be  noted  by  actual  observation. 
The  most  practical  method  of  obtaining  the  cost  of  material  for 
various  blocks  is  to  first  compute  the  cost  of  a  cubic  yard  of 
certain  proportions  of  dry-unmixed  materials,  then  by  actual 
test  ascertain  the  relative  volume  of  the  dry-unmixed  mate- 
rial to  the  wet-mixed  and  compacted  material.  It  is  then  easy 
to  find  the  cost  of  material  in  a  solid  block  of  known  dimen- 
sions, and  it  will  be  necessary  to  deduct  the  percentage  of  hol- 
low space  for  each  different  width  of  wall.  One  should  know 
exactly  how  much  the  material  costs  in  each  block  he  offers  for 
sale. 

It  is  necessary  to  know  the  average  number  of  each  kind  and 
size  of  blocks  which  a  given  number  of  men  will  produce  in  a 
day — not  the  number  they  can  produce  on  a  test  run.  It  is 
also  essential  to  know  the  various  prices  paid  labor,  and  to  con- 
sider what  labor  is  especially  chargeable  to  a  certain  grade  of 
product.  This  will  avoid  making  money  in  one  end  of  the  fac- 


124 


CONCRETE-BLOCK  MANUFACTURE. 


tory  and  losing  it  in  the  other.     The  cost  of  transporting  blocks 
from  the  yard  to  the  place  of  use  is  purely  a  local  matter,  but 


;A 


FIG.  37. — Decorative  Features  of  Two-piece  Wall. 

should  be  allowed  at  a  figure  high  enough  to  cover  breakage 
loss. 

The  items  under  Administration  and  Incidentals  are  often 


COST.  125 

overlooked  in  arriving  at  manufacturing  cost,  but  they  are  properly 
chargeable  against  the  blocks  produced,  and  there  is  not  an  item 
in  the  list  which  is  not  an  essential  expense  incident  to  the  busi- 
ness of  every  progressive  operator.  The  point  to  be  especially 
emphasized,  aside  from  the  necessity  and  consideration  of  these 
necessary  expenses  themselves,  is  that  the  amount  of  such  esti- 
mated expenditure  per  annum  should  be  charged  pro  rata  against 
the  estimated  annual  production  of  the  plant,  and  not  against 
its  utmost  capacity. 


CHAPTER  XXIII. 

ARCHITECTURE. 

PERHAPS  there  is  to-day  in  the  United  States  no  other  indus- 
try the  early  development  of  which  was  in  the  hands  of  those 
so  manifestly  unfitted  to  bring  it  to  a  high  plane  of  success.  While 
the  problems  of  useful  building  construction  were  early  solved 
in  the  designing  of  concrete-block  shapes,  and  while  a  high 
standard  of  excellence  therein  has  often  been  obtained  and  is 
adhered  to  with  more  or  less  persistence,  the  development  of 
architecture,  in  the  full  meaning  of  the  term,  has  been  a  matter 
receiving  but  little  attention.  For  this  two  valid  reasons  are 
assignable.  The  first  is  the  lack  of  recognition,  on  the  part 
of  block-makers  and  machine-manufacturers,  of  those  principles 
of  symmetry  and  decorative  fitness  which  can  alone  result  in  a 
building  beautiful  to  one  trained  to  judge  of  beauty  from  the 
view-point  of  the  architect.  The  second  is  the  lack  of  attention, 
by  architects,  to  a  building  material  the  early  examples  of  which 
repelled  them  by  the  hideous  external  appearance,  and  caused 
them  to  pass  by  on  the  other  side,  unmindful  of  the  latent  pos- 
sibilities of  this  style  of  construction,  which  only  awaited  the 
touch  of  a  master  hand  to  so  transform  it  that  buildings  beauti- 
ful and  harmonious  in  every  part  might  result. 

The  first  idea  which  presented  itself  to  the  bunglers  of  by- 
gone days  was  that  in  concrete  blocks  they  had  found  an  arti- 
ficial stone;  and  so  intent  were  they  on  impressing  the  world 

126 


ARCHITECTURE. 


127 


with  the  fact  that  it  was  really  stone  that  they  forthwith  hastened 
to  devise  ways  and  means  for  imitating  the  roughest  class  of 


stone-work.     In  this  they  overshot  the  mark,  for  the  imitation 
became  but  a  cheap  and  tawdry  thing  lacking  the  essential  variety 


128 


CONCRE TE-BLOCK  MANUFACTURE. 


ARCHITECTURE.  129 

and  naturalness  of  the  original.  There  can  be  but  one  reason 
assigned  for  the  almost  universal  survival  to  the  present  day 
of  the  prevalent  pitch-face  blocks,  and  that  is  that  the  unfinished 
and  broken  surface  makes  less  visible  the  defects  of  a  lean,  dry, 
porous,  and  ill-compacted  block.  The  successive  repetition 
throughout  a  wall  of  the  same  or  very  similar  designs  of  a  plastic 
counterfeit  of  hewn  stone  has  no  place  in  architecture.  The 
difficulty  has  been  that  block-makers  have  not  understood  that 
so-called  ornamentation  cannot  consistently  be  spread  over  a 
wall.  They  have  failed  to  recognize,  in  respect  of  decora- 
tion, the  dignity  of  plain-wall  blocks  and  their  importance  as 
an  imposing  decorative  factor.  Either  plain-wall  blocks  or 
bevel-edge  blocks  constitute  a  background  of  inestimable  value 
in  accentuating  ornamentation  for  decorative  purposes;  and 
not  only  do  they  make  better  work  a  necessity,  but  eliminate  the 
idea  of  cheap  imitation  of  a  cheap  grade  of  stone-work.  In 
this  connection  nothing  is  more  valuable  than  a  careful  study 
of  some  of  the  structures  of  the  Italian  Renaissance;  and  the 
accentuation  of  mortar-joints  in  some  of  the  block-stone  rustica- 
tion of  that  period  is  of  especial  interest  to  the  progressive  block- 
maker  of  to-day. 

In  a  previous  chapter  sufficient  consideration  has  been  given 
to  ornamental  work  and  the  methods  of  its  manufacture.  It 
is  not  within  the  scope  of  this  chapter  to  further  discuss  that 
distinct  branch  of  the  cement-block  industry,  but  rather  to  present 
for  the  operator's  consideration  the  distinction  between  orna- 
mentation and  decoration.  These  terms  are  jumbled  in  the 
mind  of  the  average  operator  in  a  manner  indicating  synonymous 
meaning.  It  must  be  comprehended  that  decoration  involves 
a  balanced  contrast  of  members  in  which  the  plainness  of  cer- 
tain portions  of  the  building  is  quite  as  essential  to  the  har- 
monious beauty  of  the  whole  as  is  the  elaborate  ornamentation. 


CHAPTER  XXIV. 

BUILDING   CONSTRUCTION. 

THE  first  consideration  of  any  system  of  building  construc- 
tion is  a  firm  foundation.  Excavation  should  be  made  to  a  soil 
of  constant  position  and  volume,  and  thereon  should  be  laid 
solid  concrete  footings  the  height  of  which  is  determined  by  the 
character  of  the  soil,  and  the  width  calculated  in  the  usual  man- 
ner by  the  resistance  of  the  soil  in  proportion  to  the  weight  to 
be  sustained.  Upon  the  footing  of  solid  and  wet  concrete,  allowed 
to  become  well  hardened,  should  be  laid  the  basement  walls  of 
concrete  blocks.  If  the  basement  walls  are  expected  to  act 
in  any  degree  as  retaining-walls,  cross-walls  should  if  possible 
divide  the  space.  If,  however,  the  intended  use  of  the  building 
renders  this  impracticable,  interior  pilasters  should  occur  at  such 
intervals  as  may  be  necessary  to  resist  the  strain  upon  the  walls. 

The  method  of  supporting  joists  and  girders  differs  with 
different  systems  of  block-manufacture,  but  usually  contem- 
plates either  a  narrower  course  of  blocks  at  joist-ends,  the  inser- 
tion of  the  joists  into  the  walls  with  small  blocks  between  joists, 
or  the  use  of  steel  stirrups  or  joist-hangers  hung  in  the  wall,  in 
much  the  same  manner  as  common  in  brick-construction.  Inas- 
much as  hollow  concrete  walls  afford  one  of  the  most  fire-resisting 
of  known  building  materials,  it  is  important  that  all  timbers 
be  hung  free,  so  that  the  failure  of  a  floor  in  case  of  interior  fire 

may  not  exert  a  strain  upon  the  walls.    Where  the  concentrated 

130 


BUILDING   CONSTRUCTION  131 

load  upon  a  given  area  of  hollow  wall  does  not  allow  a  sufficient 
factor  of  safety,  the  blocks  foj  from  one  to  three  courses  there- 
under must  be  made  solid,  or  reinforced  with  steel  sufficient  to 
increase  the  modulus  of  rupture,  so  that  the  load  may  be  dis- 
tributed throughout  the  wall. 

It  may  also  be  mentioned  that,  if  a  thoroughly  fireproof  build- 
ing be  desired,  floors  should  be  of  reinforced  concrete. 

The  width  of  wall  for  the  superstructure,  as  well  as  the  base- 
ment, will  usually  be  regulated  by  city  ordinance,  and  in  few 
places  are  widths  required  in  excess  of  those  specified  for  walls 


FIG.  40.— Metal  Wall-plug. 

of  brick.  In  the  absence  of  such  regulations  one  may  safely 
use  8",  10",  12",  and  15"  walls,  reading  in  the  order  given  for 
the  first  story  of  any  height  up  to  a  four-story  building,  and  read- 
ing inversely  for  the  thickness  of  successive  stories;  e.g.,  given 
a  three-story  building,  the  first  story  will  be  the  third  number, 
or  12",  and,  reading  inversely,  the  respective  widths  of  first,  sec- 
ond, and  third  stories  is  seen  to  be  12",  10",  and  8". 

There  is  no  especial  object  in  using  concrete-block  partitions, 
except  in  fireproof  construction.  In  that  case  they  should  be 
6"  if  bearing-partitions,  and  4"  if  not. 

In  Fig.  40  is  shown  the  device  which  is  usually  inserted  in 


I32 


CONCRETE-BLOCK  MANUFACTURE. 


mortar-joints  for  nailing  window-  and  door-trim,  base-boards, 
picture-molding,  and  the  like  to  the  walls.  It  is  very  clever, 
and  worthy  the  attention  of  every  operator. 


FIG.  41. — Various  Shapes  and  Designs. 

In  every  system  of  block-construction  there  are  a  multiplicity 
of  shapes  for  different  purposes,  such  as  corners,  window-  and 


FIG.  42. — Variety  in  Size  and  Style. 

door-jambs,  bay-window  angles,  and  arches.     In  Fig.  41  a  variety 
of  shapes  are  shown,  but  to  give  details  of  all  special  blocks 


BUILDING  CONSTRUCTION.  133 

covered  by  adjustability  of  the  many  machines  on  the  market  is 
manifestly  impossible;  and  it  is  likewise  unnecessary,  as  the 
manufacturers'  catalogues  supply  ample  information  upon  this 
matter. 

To  the  successful  maker  of  concrete  blocks  there  is  no  single 
matter  of  greater  importance  in  the  securing  of  business  and  the 
winning  of  architects'  approval  than  the  ability  to  follow  plans, 
and  to  make  from  a  blue-print  each  and  every  block  required 
for  a  building  with  such  exactness  that  no  sound  of  chisel  or 
hammer  may  be  heard  in  the  cutting  of  blocks  to  fit  their  appointed 
places.  It  must  never  be  supposed  that  an  architect  will  pre- 
pare his  plans  to  fit  the  particular  sizes  of  blocks  which  it  may 
suit  the  convenience  of  the  block-maker  to  supply.  The  latter 
must  be  able  to  make  blocks  to  fit  the  plans  of  the  architect, 
or  go  out  of  business. 


CHAPTER  XXV. 

BUILDING   REGULATIONS. 

IN  the  preparation  of  this  chapter  a  careful  review  of  all 
accessible  building  ordinances  of  the  larger  cities  in  the  United 
States  has  revealed  the  fact  that,  in  so  far  as  concerns  concrete- 
block  manufacture,  they  are  reduced  to  two  classes,  of  which 
the  most  notable  respective  examples,  and  those  indicating  the 
most  exhaustive  study  in  preparation,  are  Philadelphia  and 
Denver.  These  are  accordingly  here  represented. 

PHILADELPHIA. 

1.  Hollow  concrete  building-blocks  may  be  used  for  build- 
ings six  stories  or  less  in  height  where  said  use  is  approved  by 
the    Bureau    of    Building   Inspection,    provided,    however,    that 
such    blocks    shall   be    composed   of   at    least   one  (i)    part  of 
standard  Portland   cement,  and   not  to  exceed  five  (5)  parts  of 
clean,  coarse,  sharp  sand  or  gravel,  or  a  mixture  of  at  least  one 
part  of    Portland  cement  to  five  (5)  parts  of    crushed  rock  or 
other  suitable  aggregate;   provided  further  that  this  section  shall 
not  permit  the  use  of  hollow  blocks  in  party-walls.     Said  party- 
walls  must  be  built  solid. 

2.  All  material  to  be  of  such  fineness  as  to  pass  a  one-half- 
inch  ring,  and  be  free  from  dirt  or  foreign  matter.     The  mate- 
rial composing  such  blocks  shall  be  properly  mixed  and  manipu- 


BUILDING  REGULATIONS.  135 

lated,  and  the  hollow  space  in  said  blocks  shall  not  exceed  the 
percentage  given  in  the  following  table  for  different-height  walls, 
and  in  no  case  shall  the  walls  or  webs  of  the  block  be  less  in 
thickness  than  one-fourth  of  the  height.  The  figures  given  in 
the  table  represent  the  percentage  of  such  hollow  space  for  differ- 
ent-height walls: 

Stories  ist  26.  $d         4th          5th          6th 

i  and  2 33        33 

3  and  4 25         33         33         33 

5  and  6 20        25        25        33        33        33 

3.  The  thickness  of  walls  for  any  building  where  hollow  con- 
crete blocks  are  used  shall  not  be  less  than  is  required  by  law 
for  brick  walls. 

4.  Where  the  face  only  is  of  hollow  concrete  building-block 
and  the  backing  is  of  brick,  the  facing  of  hollow  concrete  blocks 
must  be  strongly  bonded  to  the  brick,  either  with  headers  pro- 
jecting four  inches  into  the  brick-work,  every  fourth  course  being 
a  heading  course,  or  with  approved  ties,  no  brick  backing  to 
be  less  than  eight  inches.     Where  the  walls  are  made  entirely  of 
hollow  concrete  blocks,  but  where  said  blocks  have  not  the  same 
width  as  the  wall,  every  fifth  course  shall  extend  through  the 
wall,  forming  a  secure  bond.     All  nails  where  blocks  are  used 
shall  be  laid  up  in  Portland  cement-mortar. 

5.  All    hollow  concrete   building-blocks,   before   being  used 
in  the  construction  of  any  buildings  in  the  city  of  Philadelphia, 
shall  have  attained  the  age  of  at  least  three  (3)  weeks. 

6.  Wherever  girders  or  joists  rest  upon  walls  so  that  there 
is  a  concentrated  load  on  the  block  of  over  two  (2)  tons,  the 
blocks  supporting  the  girder  or  joists  must  be  made  solid.     Where 
such  concentrated  load  shall  exceed  five  (5)  tons,  the  blocks  for 
two   (2)  courses  below,  and  for  a  distance  extending  at  least 


136  CONCRETE-BLOCK  MANUFACTURE. 

eighteen  (18)  inches  each  side  of,  said  girder  shall  be  made  solid 
Where  the  load  on  the  wall  from  the  girder  exceeds  five  (5)  tons, 
the  blocks  for  three  (3)  courses  underneath  it  shall  be  made 
solid  with  similar  material  as  in  the  blocks.  Wherever  walls 
are  decreased  in  thickness,  the  top  course  of  the  thicker  wall  to 
be  made  solid. 

7.  Provided  always  that  no  wall  or  any  part  thereof  com- 
posed of  hollow  concrete  blocks  shall  be  loaded  to  an  excess  of 
eight  (8)  tons  per  superficial  foot  of  the  area  of  such  blocks, 
including  the  weight  of  the  wall;    and  no  blocks  shall  be  used 
that  have  an  average  crushing  strength  less  than  1,000  pounds 
per  square  inch  of  area  at  the  age  of  twenty-eight  days,  no  deduc- 
tion to  be  made  in  figuring  the  area  for  the  hollow  spaces. 

8.  All  piers  and  buttresses  that  support  loads  in  excess  of 
five  (5)  tons  shall  be  built  of  solid  concrete  blocks  for  such  dis- 
tance below  as  may  be  required  by  the  Bureau  of  Building  Inspec- 
tion.    Concrete  lintels  and  sills  shall  be  reinforced  by  iron  or 
steel  rods  in  a  manner  satisfactory  to  the  Bureau  of    Building 
Inspection;    and  any  lintels  spanning  over  four  feet  six  inches 
in  the  clear  shall  rest  on  solid  concrete  blocks. 

9.  Provided   that    no  hollow  concrete   building-blocks   shall 
be  used  in  the  construction  of  any  building  in  the  city  of  Phila- 
delphia unless  the  maker  of  said  blocks  has  submitted  his  product 
to  the  full  test  required  by  the  Bureau  of  Building  Inspection, 
and  placed  on  file  with   said  Bureau  of  Building  Inspection  a 
certificate  from  a  reliable  testing-laboratory  showing  that  samples 
from  the  lot  of  blocks  to  be  used  have  successfully  passed  the 
requirements  of  the  Bureau  of  Building  Inspection,  and  filing 
a  full  copy  of  the  test  with  the  bureau. 

10.  A  brand  or  mark  of  identification  must  be  impressed  in, 
or  otherwise  permanently  attached  to,  each  block  for  purpose 
of  identification. 


BUILDING  REGULATIONS.  137 

11.  No  certificate  of  approval  shall  be  considered  in  force 
for  more  than  four  months  unless  there  be  filed  with   the  Bureau 
of  Building  Inspection  in  the  city  of  Philadelphia,  at  least  once 
every  four  months  following,  a  certification  from  some  reliable 
physical  testing-laboratory  showing  that  the  average  of  three  (3) 
specimens  tested  for  compression  and  three  (3)  specimens  tested 
for   transverse   strength   comply   with   the   requirements   of  the 
Bureau  of  Building  Inspection  of  the  city  of  Philadelphia,  said 
samples  to  be  selected  either  by  a  building-inspector  or  by  the 
laboratory  from  blocks  actually  going  into  construction  work. 
Samples  must  not  be  furnished  by  the  contractors  or  builders. 

12.  The  manufacturer  and  user  of  any  such  hollow  concrete 
blocks  as  are  mentioned  in  this  regulation,  or  either  of  them, 
shall  at  any  time  have  made  such  tests  of  the  cements  used  in 
making  such  blocks,  or  such  further  tests  of  the  completed  blocks, 
or  of  each  of  these,  at  their  own  expense,  and  under  the  super- 
vision of  the  Bureau  of  Building  Inspection,  as  the  chief  of  said 
bureau  shall  require. 

13.  The  cement  used  in  making  said  blocks  shall  be  Port- 
land  cement,   and   must   be   capable   of  passing   the   minimum 
requirements  as  set  forth  in  the   u  Standard  Specifications  for 
Cement  "  by  the  American  Society  for  Testing  Materials. 

14.  Any  and  all  blocks,  samples  of  which,  on  being  tested 
under  the  direction  of  the  Bureau  of  Building  Inspection,  fail  to 
stand  at  twenty-eight  days  the  tests  required  by  this  regulation, 
shall  be  marked  "  Condemned  "  by  the  manufacturer  or  user  and 
shall  be  destroyed. 

15.  No  concrete  blocks  shall  be  used  in  the  construction  of 
any  building  within  the  city  of  Philadelphia  until  they  shall  have 
been  inspected,  and  average  samples  of  the  lot  tested  approved 
and  accepted  by  the  chief  of  the  Bureau  of  Building  Inspection. 


138  CONCRETE-BLOCK  MANUFACTURE. 


DENVER. 

Section  167. — Blocks  of  Portland  cement  and  sand,  or  of 
Portland  cement,  sand,  and  gravel  or  crushed  stone,  may  be 
substituted  for  brick  for  building  the  walls  of  buildings  under 
the  following  conditions: 

Walls  built  of  cement- and- sand  blocks  shall  be  of  the  same 
thickness  as  specified  for  brick  walls,  except  that  the  block  walls 
may  be  8",  12",  16",  20",  and  24"  thick,  in  place  of  9",  13", 
17",  22",  26"  as  specified  for  brick. 

Walls  built  of  cement,  sand,  and  gravel,  or  crushed  stone, 
under  what  is  known  as  the  two-piece  system  of  construction, 
shall  be  of  the  same  thickness  as  specified  for  brick  walls,  except 
that  an  eight  (8)  inch  block  wall  may  be  used  in  place  of  a  nine 
(9)  inch  brick  wall,  a  ten  (10)  inch  block  wall  in  place  of  a 
thirteen  (13)  inch  brick  wall,  a  twelve  (12)  inch  block  wall  in 
place  of  a  seventeen  (17)  inch  brick  wall,  and  a  fifteen  (15)  inch 
block  wall  in  place  of  a  twenty-one  (21)  inch  brick  wall. 

Section  168. — Cement-and-sand  blocks,  made  on  the  one- 
piece  method  of  construction,  shall  not  have  hollow  spaces  exceed- 
ing one-third  (J)  the  area  of  the  block,  and  the  outer  walls 
of  the  block  shall  not  be  less  than  two  (2)  inches  thick.  The 
composition  of  the  blocks  shall  be  as  follows,  viz.: 

One  (i)  story  buildings,  one  (i)  part  Portland  cement  and 
not  more  than  five  (5)  parts  coarse,  sharp  sand. 

Two  (2)  story  buildings,  one  (i)  part  Portland  cement  and 
not  more  than  four  (4)  parts  coarse,  sharp  sand. 

Three  (3)  and  four  (4)  story  buildings  with  basement,  one 
(i)  part  Portland  cement  and  not  more  than  three  (3)  parts 
coarse,  sharp  sand. 

All  blocks  must  be  thoroughly  tamped  in  the  molds,  and  put 


BUILDING  REGULATIONS.  139 

under  a  sufficient  hydraulic  pressure  when  required  before  remov- 
ing the  block  from  the  mold. 

Section  169. — Blocks  made  on  the  two-piece  method  of  con- 
struction shall  have  an  outer  face  not  less  than  one  and  five- 
eighths  (if)  inch  thick  for  eight  (8)  inch  walls,  and  two  (2) 
inches  thick  for  ten,  twelve,  and  seventeen  (10",  12",  and 
17")  inch  walls,  and  a  center  arm  not  less  than  three  (3)  inches 
thick. 

Blocks  of  this  class  shall  be  composed  of  Portland  cement, 
sand,  and  gravel,  in  the  proportion  of  one  (i)  part  Portland 
cement  to  not  more  than  six  (6)  parts  of  sand  and  gravel  or 
broken  stone  and  not  less  than  7.8  per  cent,  water;  each  block 
shall  be  made  under  a  pressure  of  at  least  thirty  (30)  tons. 

Section  170. — No  cement  blocks  shall  be  used  in  a  building 
until  they  have  been  cured  by  being  kept  moist  for  twenty  (20) 
days  from  the  time  they  are  taken  from  the  mold,  and  said 
blocks  during  that  time  must  not  be  allowed  to  dry  out. 

Section  171. — The  building-inspector  may  at  any  time  require 
a  certified  test  of  the  cement  blocks  being  furnished  for  a  wall 
or  partition  showing  a  crushing  strength  of  at  least  one  thou- 
sand (1,000)  pounds  to  the  square  inch,  on  a  section  of  block 
nine  (9)  inches  high,  and  any  blocks  not  meeting  this  test  shall 
be  condemned  as  unfit  for  use. 

Section  172. — Chimneys  and  flues  built  of  cement  blocks 
shall  conform  to  the  requirements  for  brick  flues  as  to  flue-lining 
and  thickness  of  walls,  except  that  six  (6)  inches  of  solid  con- 
crete shall  be  considered  as  equivalent  to  eight  or  nine  (8  or  9) 
inches  of  brick- work. 

Section  173. — All  concrete  or  cement  walls  will  have  at  level 
of  floor  or  roof  timbers  a  plate  course,  to  level  each  floor,  same 
to  be  hollow,  four  (4)  by  four  (4)  inches,  all  bonded  and  set  in 
cement. 


140  CONCRETE  BLOCK  MANUFACTURE. 

All  blocks  required  for  joist-  or  beam-filling  must  be  of  the 
required  dimensions  to  fit  snug  against  and  level  with  the  top 
of  joist.  All  concrete-block  walls  and  piers  will  be  limited  to 
a  safe  load  of  ten  (10)  tons  per  square  superficial  foot;  and  all 
piers  supporting  end  of  beams,  girders,  etc.,  must  have  the  hol- 
low spaces  in  same  filled  solid  with  concrete  mixed  as  before 
specified,  and  tamped  solid  every  three  (3)  feet  in  height  as 
the  pier  is  being  built. 

Section  174. — All  centering  shall  be  self-supporting,  and  no 
center  in  concrete  construction  shall  be  struck  until  seven  (7) 
days  after  the  concrete  is  laid. 

Section  175. — All  concrete  and  cement  walls  must  be  set 
with  Portland  cement-mortar,  mixed  in  the  proportion  of  one 
(i)  part  of  cement  to  not  more  than  three  (3)  parts  of  sand; 
and  each  bed  of  cement  must  not  be  less  than  one-quarter 
(J)  inch.  Point  the  joints  on  outside  of  walls  with  similar 
cement-mortar.  All  blocks  must  break  bond  when  laid  in  the 
walls. 

Section  176. — No  materials  containing  cement,  that  may 
have  set  or  partially  set,  can  be  used  in  a  new  batch,  and  must 
be  immediately  discarded  and  thrown  out. 

All  blocks  that  may  be  damaged  or  shattered  from  the  effects 
of  cutting  or  handling  "will  not  be  allowed  to  be  used  in  any 
building,  and  must  be  removed  immediately  if  required  by  the 
building-inspector. 

Section  177. — All  structural  concrete  exposed  to  or  worked 
in  the  outer  air  shall  not  be  worked  when  the  temperature  is 
32  degrees  F.  or  less  in  the  shade;  and  any  concrete  liable 
to  be  exposed  to  frost  or  snow  or  ice,  before  it  has  attained  its 
permanent  set,  shall  be  temporarily  protected  until  the  season 
has  advanced  beyond  the  probability  of  a  frost,  or  until  the  build- 
ing is  properly  enclosed;  and  all  such  work,  after  center  is  removed, 


BUILDING  REGULATIONS.  141 

shall  be  given  a  physical  test  that  will  sustain  a  load  of  three 
(3)  times  that  for  which  it  is  designed,  without  sign  of  flaw  or 
failure. 

Upon  the  subject  of  Building  Regulations  the  following  extract 
is  made  from  an  article  by  the  author  published  in  the  Cement 
Age  of  January,  1906: 

The  rapid  growth  of  the  cement  block-industry,,  and  espe- 
cially its  introduction  in  cases  of  large  and  important  buildings 
in  great  commercial  centers,  has  awakened  great  interest  in  the 
passage  of  building  ordinances  designed  to  protect  the  public 
against  unscrupulous  operators.  In  many  places  the  tendency 
has  been  to  disregard  the  improvements  made  in  recent  years 
by  the  application  of  scientific  methods  of  proportioning,  mixing, 
compressing,  and  curing  concrete  blocks,  and  to  subject  the 
industry  to  standards  which,  if  not  entirely  fair,  were  at  least  safe 
in  those  bygone  days  when  the  art  of  concrete  construction 
was  not  based  upon  an  exact  science. 

With  the  degree  of  engineering  talent  engaged  in  the  indus- 
try at  the  present  time,  with  the  present  knowledge  of  processes 
and  methods,  and  with  the  innumerable  examples  of  satisfac- 
tory use,  it  is  as  unfair  to  the  public  as  to  the  block-makers  to 
hedge  the  industry  about  with  insane  regulations  prohibiting 
the  use  of  a  form  of  construction  at  once  strong,  durable,  and 
fireproof,  insuring  buildings  warm  in  winter,  cool  in  summer, 
dry  in  any  weather,  and  cheaper  than  any  other  standard  form 
of  building  material  of  equal  quality. 

Minneapolis  permits  the  use  of  concrete-block  walls  of  width 
equal  to  required  widths  of  brick  walls,  blocks  to  be  of  1:5  cement 
and  sand,  or  1:2:3  cement,  sand,  and  gravel  or  crushed  rock ; 
mixture  of  medium  consistency,  blocks  three  weeks  old,  hoi- 


I42  CONCRETE-BLOCK  MANUFACTURE. 

low  spaces  from  33%  to  25%  according  to  height  of  walls,  mini- 
mum crushing  strength  700  Ibs.  per  square  inch. 

Newark  requires  1:1^:2^  of  standard  Portland  cement, 
sharp-grit  sand  free  from  loam  or  dirt,  and  crushed  stone,  slag, 
or  gravel,  all  to  pass  j"  screen ;  maximum  dimensions  of  blocks, 
36"Xio"Xi6";  minimum  width  of  wall,  8";  maximum  hollow 
space,  33 \%\  blocks  30  days  old,  tensile  test  150  Ibs.,  com- 
pression 1500  Ibs. 

Philadelphia  provides  for  i :  5  mixture,  using  any  suitable 
aggregate;  hollow  space  from  33%  to  20%,  decreasing  in  the 
lower  stories  as  the  walls  increase  in  height;  same  width  of  wall 
as  for  brick;  solid  blocks  under  concentrated  loads;  and  blocks 
to  be  three  weeks  old.  The  transverse,  compression,  absorption, 
freezing,  and  fire  tests  adopted  by  the  Philadelphia  bureau  prob- 
ably constitute  the  most  careful  revision  yet  made  of  the  build- 
ing-material tests  of  the  Borough  of  Manhattan,  the  changes 
adapting  the  specifications  to  concrete-block  construction. 

Without  any  desire  to  criticise  the  excellent  work  of  those 
eminent  gentlemen  who  have  prepared  ordinances  in  the  cities 
named,  the  author  wishes  to  mention  a  few  pertinent  points 
worthy  the  consideration  of  those  who  may  have  occasion  to  pre- 
pare like  regulations. 

A  mixture  of  1:1^:2^,  1:2:3  or  1:5,  unless  qualified,  is 
Indeterminate.  Unless  expressly  stated  to  the  contrary,  these 
proportions  are  generally  understood  to  be  by  volume,  and  it 
must  be  remembered: 

1.  That  the  volume  of  cement  varies  from  0.78  cu.  ft.  packed 
to  i  cu.  ft.  loose. 

2.  That,  in  practice,  sand  is  never  dried  to  constant  volume; 
that  its  volume  increases  with  addition  of  moisture;  and  that 
the  volume  of  fine  sand  increases  more  rapidly  with  moisture 
than  does  coarse  sand. 


BUILDING  REGULATIONS.  143 

3.  That,  if  an  aggregate  be  of  uniform  size  and  rounded  par- 
ticles, it  is  difficult  in  practice  to  secure  more  than  56%  of  solids; 
while,  if  the  aggregate  be  correctly  graded,  the  porosity  may  be 
decreased  indefinitely. 

.It  is  therefore  evident  that  all  specifications  cited  are  defec- 
tive, inasmuch  as  proportions  are  not  specified  by  weight. 

Again,  given  proportions  may  be  ideal  in  one  locality  and 
totally  wrong  when  applied  to  the  local  materials  of  another 
section.  This  fact  will  be  appreciated  by  every  cement-worker 
of  wide  experience,  and  the  author  has  found  it  thoroughly 
exemplified  in  his  visits  to  plants  throughout  the  country.  It  is 
absolutely  necessary  that  the  required  proportions  to  secure 
greatest  strength,  durability,  density,  and  impermeability  with 
a  minimum  quantity  of  cement  be  determined  by  expert  tests 
upon  local  materials.  The  cost  of  such  tests  is  infinitesimal 
in  comparison  to  the  saving  in  manufacturing  cost  and  the  marked 
increase  in  quality. 

The  amount  of  water  should  be  clearly  specified.  It  is  folly 
to  suppose  that  block-makers  will  always  take  the  trouble — for 
under  many  methods  it  is  trouble — to  use  the  proportion  of 
water  necessary  to  secure  the  full  strength  of  the  cement.  Either 
a  certain  percentage  of  water  should  be  stated,  or  recourse  should 
be  had  to  the  ordinary  engineering  specifications  governing  the 
three  degrees  of  moisture  in  concrete.  Normal  consistency, 
like  correct  proportioning  of  the  aggregate,  is  a  matter  for  expert 
determination  based  on  local  conditions. 

It  is  insufficient  to  say  that  blocks  be  three  weeks  or  thirty 
days  old.  They  must  be  CURED,  and  curing  means  more  than 
age.  It  covers  the  most  important  period  in  block-manufacture; 
and  it  is  essential  that  blocks  receive,  during  this  time,  such 
scientific  treatment  as  will  lift  the  concrete-block  industry  to  a 
higher  plane. 


144  CONCRETE-BLOCK  MANUFACTURE. 

The  maximum  percentage  of  hollow  space  is  arbitrarily 
fixed  at  a  figure  which  is  unjust  to  an  honest  and  intelligent  manu- 
facturer. This  percentage  should  be  in  the  nature  of  a  sliding- 
scale  based  on  compressive  and  transverse  tests.  There  are 
many  manufacturers  marketing  blocks  which,  with  50%  or  55% 
of  air-space  in  the  walls,  afford  greater  safety  than  blocks  passing 
the  requirements  of  the  Philadelphia  ordinance  would  afford 
with  25%  of  hollow  space.  The  best  authorities  are  agreed 
that  properly  made  concrete  will  at  four  weeks  show  over  2,000 
Ibs.  resistance  to  compression,  and  over  3,000  Ibs.  at  one  year. 
As  a  matter  of  fact,  blocks  28  days  old  have  tested  2,600  Ibs. 
It  is  manifestly  unfair  to  restrict  such  blocks  to  the  same  per- 
centage of  hollow  space  as  blocks  having  an  average  crushing 
strength  of  1,000  Ibs.  per  square  inch. 

Relative  to  widths  of  walls,  the  standard  specification,  "  equal 
in  their  combined  width  to  the  thicknesses  required  for  brick 
walls,"  is  manifestly  unjust.  The  most  eminent  American 
authority  on  concrete  architecture  has  rendered  an  opinion  that 
a  i  o"  wall  of  properly  made  and  properly  bonded  concrete  blocks, 
laid  in  cement-mortar,  possesses  ample  strength  for  three-story 
construction,  and  a  15"  wall  for  six  stories.  There  is  no  doubt 
about  an  8"  wall  of  good  concrete  blocks  being  strong  enough 
for  two-story  construction,  if  the  wall  be  laid  in  such  manner 
that  lateral  stress  is  resisted  by  an  efficient  bond.  The  widths 
given  in  the  author's  paper  published  in  the  Engineering  News 
of  October  5,  1905,  are  8"  for  one  story,  10"  for  two  stories, 
12"  and  10"  for  three  stories,  and  15",  12"  and  10"  for  four 
stories.  These  may  be  regarded  as  conservative. 


CHAPTER  XXVI. 

MANUFACTURE   OF   ACCESSORIES. 

THE  manufacture  of  sills,  lintels,  columns,  caps,  and  other 
portions  of  buildings  which  may  not  be  accurately  termed  build- 
ing-blocks constitutes  an  important  item  in  the  work  of  every 
block-maker,  not  only  because  of  their  necessity  in  construction, 
but  because  of  the  relatively  large  profit  obtainable  by  reason 
of  the  fact  that  they  come  into  direct  competition  with  the  finest 
cut  stone.  It  is  not  usual  for  the  standard-block  machines  to 
make  provision  for  this  class  of  work,  and  recourse  must  be 
had  to  accessory  equipment  or  local  devices  for  manufacturing 
these  members. 

Fig.  43  shows  one  of  the  later  and  more  practical  sill-molds. 
The  method  of  manufacture  is  similar  to  that  employed  in  oper- 
ating the  building-block  mold  shown  in  Fig.  16,  inasmuch  as  the 
mold  is  moved  without  disturbing  the  newly  made  sill.  In  the 
illustration  the  sides  and  ends  are  each  i  J"  from  the  sill,  and  the 
mold  is  ready  to  be  lifted  away,  leaving  the  sill  to  cure  on  the 
board  on  which  it  was  manufactured. 

In  many  block  factories  it  is  preferred  to  make  the  molds 
for  this  class  of  work,  using  therefor  lumber  surfaced  on  one 
side  and  carefully  sandpapered  and  shellacked;  thus  not  only 
rendering  the  wood  wateiproof  and  preventing  warping,  but 
also  overcoming  the  impression  of  the  grain  in  the  wood  upon 
the  molded  sill.  If  this  course  be  adopted,  the  sides  should 


146 


CONCRETE-BLOCK  MANUFACTURE. 


have  cleats  to  engage  the  ends,  and  a  clamp  should  hold  the  sides 
in  place    at  either  end.     A  bottom-board  of  dimensions  some- 


FIG.  43. — Cement  Sill-mold. 

what  greater  than  those  of  the  sill  should  be  used.  The  face- 
matter  should  be  put  on  the  bottom  and  sides,  and  backed  with 
coarse  concrete  as  wet  as  can  be  tamped.  When  the  sides  are 


MANUFACTURE  OF  ACCESSORIES.  147 

undamped  and  removed,  the  molded  sill  is  left  on  the  bottom- 
board,  face  down,  until  hard  enough  to  permit  of  handling,  and 
this  time  will,  owing  to  the  size  and  weight  of  the  member  and 
the  fact  of  its  being  without  hollow  space,  be  much  longer  than 
required  for  an  ordinary  building-block.  It  will  be  noted  that 
this  method  of  molding  the  face  is  decidedly  more  favorable 
to  sound  and  durable  work  than  the  customary  manner  of  molding 
the  sill  face-up  and  troweling  the  surface,  as  'the  latter  prac- 
tice draws  neat  cement  to  the  surface  and  results  in  hair-  or  map- 
cracks.  These  home-made  molds  may  be  varied  by  the  inser- 
tion of  thin  wedge-shape  strips  before  depositing  the  face-matter, 
to  give  any  required  bevel  to  the  sill. 

In  molds  of  similar  construction,  by  making  one  end-piece 
longer  than  the  opposite  end-piece,  any  desired  radius  may  be 
obtained  for  arch-blocks  and  keystones.  In  making  members 
requiring  a  molded  effect,  the  insertion  of  any  pattern  of  stock- 
molding,  in  the  same  manner  suggested  for  the  wedge-shape 
strips  in  the  case  of  sills,  will  produce  handsome  results. 

The  more  ornamental  members,  such  as  columns,  caps, 
balusters,  and  the  like,  may  be  cast  in  sand  or  plaster,  in  the  man- 
ner already  described  in  the  chapter  on  Ornamentation,  although, 
if  any  considerable  number  are  required,  it  will  prove  more  eco- 
nomical to  purchase  iron  molds  for  the  purpose.  These  molds 
are  comparatively  easy  of  operation,  and,  while  constructed  on 
lines  preserving  the  beauty  of  the  original  pattern,  eliminate 
any  undercutting  in  order  to  secure  perfect  release. 

Figs.  44  and  45  show  a  few  of  the  designs  for  which  iron 
molds  are  obtainable.  It  is  especially  desirable  that  the  one 
who  is  entering  upon  the  manufacture  of  concrete  blocks  be 
equipped  with  molds  for  making  some  of  the  more  attractive 
pieces,  as  the  ability  to  show  work  of  this  class  will  disclose  to 
builders  the  adaptability  of  concrete  blocks  for  ornate  construe- 


148 


CONCRETE-BLOCK  MANUFACTURE. 


Column. 


Ball  and  Base. 
FIG.  44. — Ornamental  Accessories. 


Balusters. 


MANUFACTURE  OF  ACCESSORIES. 


149 


tion;  and  the  relatively  low  cost  of  this  work  in  comparison  with 
the  same  patterns  in  cut  stone  will  secure  ready  consideration 
from  the  public.  It  will  be  found  that  the  maintenance  of  a 


FIG.  45. — Porch  Column  and  Balustrade. 

good  exhibit  of  this  class  of  work  will  have  the  twofold  effect 
of  directing  the  attention  of  prospective  builders  to  the  possi- 
bilities of  concrete-block  construction,  and  of  selling  considerable 
numbers  of  these  special  pieces  for  use  in  buildings  constructed 
of  ordinary  building  materials. 


INDEX. 


Absorption  tests,  97 
Adulterants,  16 
Aggregate,  8 

division  of,  9 
Arrangement  of  plant,  75 
Artificial  stone,  126 

Belt  conveyors,  78 
Broken  stone,  II 

Caps,  145 
Cars,  76 

Casting  in  sand,  45 
Cement,  history  of,  4 
natural,  5 
Parker's,  4 
Portland,  6 

ingredients,  6 
process  of  manufac- 
ture, 7 

raw  materials,  6 
testing,  8 
weight  of,  122 
Puzzolan,  4 
Roman,  4 
slag,  5 

Chemicals,  18 
Cinder  concrete,  12 
Color,  influence  of  curing  on,  6 1 
Colors,  19 
Columns,  145 
Common  labor,  82 
Compression  tests,  97 
Computation  of  cost,  122 
Concrete,  definition,  I 

general  theory,  2 
Consistency,  48 
Constancy  of  volume,  8 
Cost,  method  of  determining,  122 


Crystallization,  48,  59 

Curing,  importance  of  scientific,  59 

steam,  63 

uniform  conditions  of,  60 

yard,  78 

Decoration,  129 

Density,  89' 

Denver  building  regulations,  138 

Determination  of  vo,ds,  22 

Durability,  94 

Errors  of  manufacturers,  117 
of  opera  tors,  119 

Face-down  machine,  69 
Face,  form  of,  54 
Facing,  51 

color  of,  52 
Fire  resistance,  91 

test,  98 
Footings,  130 
Foreman,  80 
Freezing  test,  98 

Gradation  of  sand,  IO 
Gravel,  n 

Hand  tamping,  44 

Heat  conductivity,  31 

Hollow  blocks,  various  shapes  of,  34 

Hose,  use  of,  78 

Hydra  ted  lime,  17 

Impermeability,  90 

Joists,  method  of  supporting,  130 

Lime,  hydra  ted,  17 


INDEX. 


Lintels,  145 

Loam  or  clay  in  sand,  10 

Machines,  classification  of,  64 

objects  of,  65 
Masons,  82 

Metal  ties,  blocks  containing,  35 
Minneapolis  building  regulations,  141 
Mixers,  batch,  27 

continuous,  27 
Mixing,  hand,  26 

importance  of  thorough,  24 
machine,  27 
Mixture,  dry,  49 

medium,  49 
wet,  50 
Modeler,  82 
Mold -maker,  81 
Molds,  movable,  68 

sill,  146 

Monolithic  construction,  2 
Multiple  air-space,  39 

Nailing-plugs,  131 

Newark  building  regulations,  142 

Ornamentation,  129 

processes   of  manufac- 
ture, 56 
Overhead  bins,  78    ' 

Partitions,  131 

Philadelphia  building  regulations,  134 

tests,  96 
Pilasters,  130 
Plans,  working  to,  133 
Pneumatic  tamping,  44 
Porosity,  causes  of,  85 
Pouring,  45 
Press,  mechanical,  72 
Pressure,  hydraulic,  46 

mechanical,  46 
Processes  of  manufacture,  43 
Proportioning,  general  principles  of,  21 
Proportions,  for  facing,  52 

how  expressed,  20 


Proportions,  importance  of  correct,  20 
method  of  determining,  22 

Rock  face,  1 29 
Roll-over  mold,  66 

Salt  in  mixing  water,  14 
Sand,  cleanness,  10 

gradation  of  sizes,  10 

mineralogy  unimportant,  9 

shape  of  grain,  9 

size  of  grain,  10 

strength  and  firmness,  9 

washing,  10 
Sills,  145 
Soundness,  87 

of  cement,  how  determined 

6 

Specific  gravity  of  aggregate,  22 
Sprinkling  blocks,  61 
Staggered  air-space,  40 
Stone,  broken,  n 

screenings,  II 
Strength,  88 
Sun,  exposure  of  green  blocks  to,  60 

Testing,  cement,  8 

sand,  9 

Transverse  tests,  97 
Two-piece  blocks,  36 

Upright  machine,  67 

Ventilation,  33,  94 
Voids,  determination  of,  22 
elimination  of,  84 


Walls,  advantages  of  hollow,  3 

width  of,  131,  135,  138 
Washing  sand,  10 
Water,  addition  of  salt  to,  14 

curing,  60 

purity,  13 

quantity,  13 

Waterproofing  compounds,  18 
Winter,  curing  in,  63 

manufacture,  79 


144 


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Furman's  Manual  of  Practical  Assaying 8vo,  3  oo 

*  Getman's  Exercises  in  Physical  Chemistry i2mo,  2  oo 

Gill's  Gas  and  Fuel  Analysis  for  Engineers i2mo,  i  25 

Grotenfelt's  Principles  of  Modern  Dairy  Practice.     (Woll.) i2mo,  2  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) i2mo,  i  25 

Hammarsten's  Text-book  of  Physiological  Chemistry.     (Mandel.) 8vo,  4  oo 

Helm's  Principles  of  Mathematical  Chemistry.     (Morgan.) i2mo,  i  50 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Hind's  Inorganic  Chemistry 8vo,  3  o-~ 

*  Laboratory  Manual  for  Students I2mo,  i  oo 

Holleman's  Text-book  of  Inorganic  Chemistry.     (Cooper.) 8vo,  2  50 

Text-book  of  Organic  Chemistry.     (Walker  and  Mott.) 8vo,  2  50 

*  Laboratory  Manual  of  Organic  Chemistry.     (Walker.) i2mo,  i  oo 

Hopkins's  Oil-chemists'  Handbook 8vo,  3  oo 

Jackson's  Directions  for  Laboratory  Work  in  Physiological  Chemistry.  .8vo,  i  25 

Keep's  Cast  Iron 8vo,  2  50 

Ladd's  Manual  of  Quantitative  Chemical  Analysis *.....  I2mo,  i  oo 

Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

*  Langworthy  and  Austen.         The   Occurrence   of  Aluminium  in  Vege  able 

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Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control, 8vo,  7  50 

Lob's  Electrochemistry  of  Organic  Compounds.  (Lorenz.) 8vo,  3  oo 

Lodge's  Notes  on  Assaying  and  Metallurgical  Laboratory  Experiments.  ..  .8vo,  3  oo 

Low's  Technical  Method  of  Ore  Analysis 8vo.  3  oo 

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4 


*  McKay  and  Larsen's  Principles  and  Practice  of  Butter-making 8vo  i  50 

Mandel's  Handbook  for  Bio-chemical  Laboratory I2mo,  i  50 

*  Martin's  Laboratory  Guide  to  Qualitative  Analysis  with  the  Blowpipe .  .  I2mo,  60 
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Matthew's  The  Textile  Fibres 8vo,  3  50 

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Miller's  Manual  of  Assaying '. i2mo,  oo 

Cyanide  Process i2mo,  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.) .  .  .  .  i2mo,  50 

Mixter's  Elementary  Text-book  of  Chemistry i2mo,  50 

Morgan's  An  Outline  of  the  Theory  of  Solutions  and  its  Results i2mo,  oo 

Elements  of  Physical  Chemistry i2mo,  3  oo 

*  Physical  Chemistry  for  Electrical  Engineers i2mo,  i  50 

Morse's  Calculations  used  in  Cane-sugar  Factories i6mo,  morocco,  i  50 

Mulliken's  General  Method  for  the  Identification  of  Pure  Organic  Compounds. 

Vol.  I Large  8vo,  5  oo 

O'Brine's  Laboratory  Guide  in  Chemical  Analysis 8vo,  2  oo 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Ostwald's  Conversations  on  Chemistry.     Part  One.     (Ramsey.) i2mo,  i  50 

"                    "                "           "              Part  Two.     (Turnbull.) I2mo,  200 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

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Pinner's  Introduction  to  Organic  Chemistry.     (Austen.) I2mo:  i  50 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oc 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
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*  Reisig's  Guide  to  Piece-dyeing 8vo,  25  oo 

Richards  and  Woodman's  Air.Water,  and  Food  from  a  Sanitary  Standpoint.  .8vo,  2  oo 
Ricketts  and  Russell's  Skeleton  Notes  upon  Inorganic  Chemistry.     (Part  I. 

Non-metallic  Elements.) 8vo,  morocco,  75 

Ricketts  and  Miller's  Notes  on  Assaying 8vo,  3  oo 

Rideal's  Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  3  50 

Disinfection  and  the  Preservation  of  Food 8vo,  4  oo 

Riggs's  Elementary  Manual  for  the  Chemical  Laboratory 8vo,  i  25 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Rostoski's  Serum  Diagnosis.     (Bolduan.) I2mo,  i  oo 

Ruddiman's  Incompatibilities  in  Prescriptions 8vo,  2  oc 

*  Whys  in  Pharmacy I2mo,  i  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Salkowski's  Physiological  and  Pathological  Chemistry.     (Orndorff.) 8vo,  2  50 

Schimpf's  Text-book  of  Volumetric  Analysis I2mo,  2  50 

Essentials  of  Volumetric  Analysis i2mo,  i  25 

*  Qualitative  Chemical  Analysis 8vo,  i  25 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students „ . .  8vo,  2  50 

Spencer's  Handbook  for  Chemists  of  Beet-sugar  Houses i6mo,  morocco,  3  oo 

Handbook  for  Cane  Sugar  Manufacturers i6mo,  morocco,  3  oo 

Stockbridge's  Rocks  and  Soils 8vo,  2  50 

*  Tillman's  Elementary  Lessons  in  Heat 8vo,  i  50 

*  Descriptive  General  Chemistry , 8vo,  3  oo 

Treadwell's  Qualitative  Analysis.     (Hall.) 8vo,  3  oo 

Quantitative  Analysis.     (Hall.) 8vo,  4  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Van  Deventer's  Physical  Chemistry  for  Beginners.     (Boltwood.) I2mo,  i  50 

*  Walke's  Lectures  on  Explosives 8vo,  4  oo 

Ware's  Beet-sugar  Manufacture  and  Refining .  .Small  8vo,  cloth,  4  oo 

Washington's  Manual  of  the  Chemical  Analysis  of  Rocks 8vo,  2  oo 

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Wassermann's  Immune  Sera :  Haemolysins,  Cytotoxins,  and  Precipitins.    (Bol- 

duan.) i2mo,  T  oo 

Weaver's  Military  Explosives 1 8vo,  3  oo 

Wehrenfennig's  Analysis  and  Softening  of  Boiler  Feed- Water .8vo,  4  oo 

Wells's  Laboratory  Guide  in  Qualitative  Chemical  Analysis 8vo,  i  50 

Short  Course  in  Inorganic  Qualitative  Chemical  Analysis  for  Engineering 

Students i2mo,  i  50 

Text-book  of  Chemical  Arithmetic I2mo,  i  25 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

Wilson's  Cyanide  Processes i2mo,  i  50 

Chlorination  Process I2mo,  i  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo,  7  50 

Wulling's    Elementary    Course    in  Inorganic,  Pharmaceutical,  and  Medical 

Chemistry, i2mo,  2  oo 


CIVIL  ENGINEERING. 

BRIDGES    AND    ROOFS.       HYDRAULICS.       MATERIALS    OF    ENGINEERING. 
KAIL  WAY  ENGINEERING. 

Baker's  Engineers'  Surveying  Instruments I2mo,  3  oo 

Bixby's  Graphical  Computing  Table Paper  ig£  X24i  inches.  25 

**  Burr's  Ancient  and  Modern  Engineering  and  the  Isthmian  Cana ..     (Postage, 

27  cents  additional.) 8vo,  3  50 

Comstock's  Field  Astronomy  for  Engineers. 8vo,  2  50 

Davis's  Elevation  and  Stadia  Tables 8vo,  i  oo 

Elliott's  Engineering  for  Land  Drainage I2mo,  i  50 

Practical  Farm  Drainage i2mo,  i  oo 

*Fiebeger's  Treatise  on  Civil  Engineering 8vo,  5  oo 

Flemer's  Phototopographic  Methods  and  Instruments 8vo,  5  oo 

Folwell's  Sewerage.     (Designing  and  Maintenance.) 8vo,  3  oo 

Freitag's  Architectural  Engineering.     2d  Edition,  Rewritten 8vo,  3  50 

French  and  Ives's  Stereotomy 8vo,  2  50 

Goodhue's  Municipal  Improvements I2mo,  i  75 

Goodrich's  Economic  Disposal  of  Towns'  Refuse 8vo,  3  50 

Gore's  Elements  of  Geodesy 8vo,  2  50 

Hayford's  Text-book  of  Geodetic  Astronomy 8vo,  3  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Howe's  Retaining  Walls  for  Earth i2iro,  i   25 

*  Ives's  Adjustments  of  the  Engineer's  Transit  and  Level. i6mo,  Bds.  25 

Ives  and  Hilts's  Problems  in  Surveying i6mo,  morocco,  i  50 

Johnson's  ( J.  B.)  Theory  and  Practice  of  Surveying Small  8vo,  4  oo 

Johnson's  (L.  J.)  Statics  by  Algebraic  and  Graphic  Methods 8vo,  2  oo 

Laplace's  Philosophical  Essay  on  Probabilities.     (Truscott  and  Emory.) .  i2mo,  2  oo 

Mahan's  Treatise  on  Civil  Engineering.     (1873.)     (Wood.) 8vo,  5  oo 

*  Descriptive  Geometry 8vo,  i  50 

Merriman's  Elements  of  Precise  Surveying  and  Geodesy 8vo,  2  50 

Merriman  and  Brooks's  Handbook  for  Surveyors i6mo,  morocco,  2  oo 

Nugent's  Plane  Surveying 8vo,  3  50 

Ogden's  Sewer  Design , i2mo,  2  oo 

Parsons's  Disposal  of  Municipal  Refuse 8vo,  2  oo 

Patton's  Treatise  on  Civil  Engineering 8vo  half  leather,  7  50 

Reed's  Topographical  Drawing  and  Sketching 4*0,  5  oo 

Rideal's  Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  3  50 

Siebert  and  Biggin's  Modern  Stone-cutting  and  Masonry 8vo,  i  50 

Smith's  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

Sondericker's  Graphic  Statics,  with  Applications  to  Trusses,  Beams,  and  Arches. 

8vo,  2  oo 

6 


Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced 8vo,  5  oo 

*  Trau twine's  Civil  Engineer's  Pocket-book i6mo,  morocco,  5  oo 

Venable's  Garbage  Crematories  in  America 8vo,  2  oo 

Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  co 

Sheep,  6  50 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  8vo,  5  oo 

Sheep,  5  50 

Law  of  Contracts 8vo,  3  oo 

Warren's  Stereotomy — Problems  in  Stone-cutting 8vo,  2  50* 

Webb's  Problems  in  the  Use  and  Adjustment  o2  Engineering  Instruments. 

i6mo,  morocco,  i  25 

Wilson's  Topographic  Surveying 8vo,  3  50 


BRIDGES  AND  ROOFS. 

Boiler's  Practical  Treatise  on  the  Construction  of  Iron  Highway  Bridges.  .8vo,  2  oo 

*       Thames  River  Bridge 4to,  paper,  5  oo 

Burr's  Course  on  the  Stresses  in  Bridges  and  Roof  Trusses,  Arched  Ribs,  and 

Suspension  Bridges 8vo,  3  50 

Burr  and  Falk's  Influence  Lines  for  Bridge  and  Roof  Computations 8vo,  3  o» 

Design  and  Construction  of  Metallic  Bridges 8vo.  5  oo 

Du  Bois's  Mechanics  of  Engineering.     Vol.  II £rrall  4to,  10  oo 

Foster's  Treatise  on  Wooden  Trestle  Bridges 4to,  5  oo 

Fowler's  Ordinary  Foundations 8vo,  3  50 

Greene's  Roof  Trusses 8vo,  i  25 

Bridge  Trusses r\  . . .  Svo,  2  50 

Arches  in  Wood,  Iron,  and  Stone 8vo5  2  50 

Howe's  Treatise  on  Arches • Svo,  4  oo 

Design  of  Simple  Roof- trusses  in  Wood  and  Steel Svo,  2  oo 

Symmetrical  Masonry  Arches Svo,  2  50 

Johnson,  Bryan,  and  Turneaure's  Theory  and  Practice  in  the  Designing  of 

Modern  Framed  Structures.. . Small  4to,  10  oo 

Merrlman  and  Jacoby's  Text-book  on  Roofs  and  Bridges: 

Part  I.     Stresses  in  Simple  Trusses Svo,  2  50 

Part  II.    Graphic  Statics Svo,  2  50 

Part  III.  Bridge  Design Svo,  2  50 

Part  IV.   Higher  Structures Svo,  2  50 

Morison's  Memphis  Bridge 4to,  10  oo 

Waddell's  De  Pontibus,  a  Pocket-book  for  Bridge  Engineers.  .i6mo,  rrorocco,  2  oo 

*  Specifications  for  Steel  Bridges , i2iro,  50 

Wright's  Designing  of  Draw-spans.     Two  parts  in  one  volume Svo,  3  5° 


HYDRAULICS. 

Barnes's  Ice  Formation Svo,  3  oo 

Bazin's  Experiments  upon  the  Contraction  of  the  Liquid  Vein  Issuing  from 

an  Orifice.     (Trautwine.) Svo,  2  oo 

Bovey's  Treatise  on  Hydraulics Svo,  5  oo 

Church's  Mechanics  of  Engineering Svo,  6  oo 

Diagrams  of  Mean  Velocity  of  Water  in  Open  Channels paper,  i  50 

Hydraulic  Motors Svo,  2  oo 

Coffin's  Graphical  Solution  of  Hydraulic  Problems i6mo,  morocco,  2  50 

Flather's  Dynamometers,  and  the  Measurement  of  Power : I2mo,  3  oo 

Folwell's  Water-supply  Engineering Svo,  4  oo 

Frizell's  Water-power Svo,  5  oo 

7 


Fuertes's  Water  and  Public  Health „ ,  121110,  i  50 

Water-filtration  Works 12010,  2  50 

Ganguillet  and  Kutter's  General  Formula  for  the  Uniform  Flow  of  Water  in 

Rivers  and  Other  Channels.     (Bering  and  Trautwine.) 8vo,  4  oo 

Hazen's  Filtration  of  Public  Water-supply 8vo,  3  oo 

Hazlehurst's  Towers  and  Tanks  for  Water-works 8vo,  2  50 

Herschel's  115  Experiments  on  the  Carrying  Capacity  of  Large,  Riveted,  Metal 

Conduits 8vo,  2  oo 

Mason's  Water-supply.     (Considered  Principally  from  a  Sanitary  Standpoint.) 

8vo,  4  oo 

Merriman's  Treatise  on  Hydraulics 8vo,  5  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oo 

Schuyler's   Reservoirs  for  Irrigation,   Water-power,  and   Domestic   Water- 
supply Large  8vo,  5  oo 

**  Thomas  and  Watt's  Improvement  of  Rivers      (Post.,  44C.  additional.)  4to,  6  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Wegmann's  Design  and  Construction  of  Dams \ 4to,  5  oo 

Water-supply  of  the  City  of  New  York  from  1658  to  1895 4to,  10  oo 

Williams'  and  Hazen's  Hydraulic  Tables 8vo,  i  50 

Wilson's  Irrigation  Engineering Small  8vo,  4  oo 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Turbines 8vo,  2  50 

Elements  of  Analytical  Mechanics 8vo,  3  oo 


MATERIALS  OF  ENGINEERING. 

Baker's  Treatise  on  Masonry  Construction 8vo,  5  oo 

Roads  and  Pavements 8vo,  5  oo 

Black's  United  States  Public  Works Oblong  4to,  5  oo 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering 8vo,  7  50 

Byrne's  Highway  Construction 8vo,  5  oo 

Inspection  of  the  Materials  and  Workmanship  Employed  in  Construction. 

i6mo>  3  oo 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Du  Bois's  Mechanics  of  Engineering.     Vol.  I Small  4to,  7  50 

*Eckel's  Cements,  Limes,  and  Plasters 8vo,  6  oo 

Johnson's  Materials  of  Construction Large  8vo,  6  oo 

Fowler's  Ordinary  Foundations 8vo,  3  50 

Graves's  Forest  Mensuration 8vo,  4  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Keep's  Cast  Iron 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  50 

Marten's  Handbook  on  Testing  Materials.     (Henning.)     2  vols 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

-Merrill's  Stones  for  Building  and  Decoration 8vo,  5  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

Strength  of  Materials i2mo,  i  oo 

Metcalf's  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Patton's  Practical  Treatise  on  Foundations 8vo,  5  oo 

Richardson's  Modern  Asphalt  Pavements 8vo,  3  oo 

Richey's  Handbook  for  Superintendents  of  Construction i6mo,  mor.,  4  oo 

*  Ries's  Clays:  Their  Occurrence,  Properties,  and  Uses 8vo,  5  oo 

Rockwell's  Roads  and  Pavements  in  France I2mo,  i  25 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Smith's  Materials  of  Machines i2mos  i  oo 

Snow's  Principal  Species  of  Wood 8vo,  3  50 

8 


Spalding's  Hydeawlic  Cement I2mo,  2  oo 

Text-book  on  Roads  and  Pavements 12010,  2  oo 

Taylor  and  Thompson's  Treatise  on  Concrete.  Plain  and  Reinforced 8vo,  5  oo 

Thurston's  Materials  of  Engineering.     3  Parts 8vo,  8  oo 

Parti.     Non-metallic  Materials  of  Engineering  and  Metallurgy 8vo,  2  oo 

Part  II      Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents.  .    8vo,  2  50 

Thurston's  Text-book  of  the  Materials  of  Construction t 8vo,  5  oo 

Tillson's  Street  Pavements  and  Paving  Materials 8vo,  4  oo 

Waddell's  De  Pontibus     (A  Pocket-book  for  Bridge  Engineers.).  .  i6mo,  mor.,  2  oo 

Specifications  for  Steel  Bridges i2mo,  i  25 

Wood's  (De  V.)  Treatise  on  the  Resistance  of  Materials,  and  an  Appendix  on 

the  Preservation  of  Timber 8vo,  2  oo 

Wood's  (De  V.)  Elements  of  Analytical  Mechanics 8vo,  $  oo 

Wood's  (M.  P.)  Rustless  Coatings;    Corrosion  and  Electrolysis  of  Iron  and 

Steel,.  8vo,  4    oo 


RAILWAY  ENGINEERING. 

Andrew's  Handbook  for  Street  Railway  Engineers 3x5  inches,  morocco,  i  25 

Berg's  Buildings  and  Structures  of  American  Railroads 4to,  5  oo 

Brook's  Handbook  of  Street  Railroad  Location i6mo,  morocco,  i  50 

Butt's  Civil  Engineer's  Field-book i6mo,  morocco,  2  50 

Crandall's  Transition  Curve i6mo,  morocco,  i  50 

Railway  and  Other  Earthwork  Tables .  8vo,  i  50 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book     i6mo,  morocco,  5  oo 

Dredge's  History  of  the  Pennsylvania  Railroad:   (1879) Paper,  5  oo 

*  Drinker's  Tunnelling,  Explosive  Compounds,  and  Rock  Drills. 4to,  half  mor.,  25  oo 

Fisher's  Table  of  Cubic  Yards Cardboard,  25 

Godwin's  Railroad  Engineers'  Field-book  and  Explorers'  Guide.  .  .  i6mo,  mor.,  2  50 

Howard's  Transition  Curve  Field-book i6mo,  morocco,  i  50 

Hudson's  Tables  for  Calculating  the  Cubic  Contents  of  Excavations  and  Em- 
bankments  8vo,  i  oo 

Molitor  and  Beard's  Manual  for  Resident  Engineers.  , i6mo,  i  oo 

Nagle  s  Field  Manual  for  Railroad  Engineers i6mo,  morocco.  3  oo 

Philbrick's  Field  Manual  for  Engineers.  . i6mo,  morocco,  3  oo 

Searles's  Field  Engineering i6mo,  morocco,  3  oo 

Railroad  Spiral i6mo,  morocco,  i  50 

Taylor's  Prismoidal  Formulae  and  Earthwork 8vo,  i  50 

*  Trautwine's  Method  of  Calculating  the  Cube  Contents  of  Excavations  and 

Embankments  by  the  Aid  of  Diagrams 8vo,  2  oo 

The  Field  Practice  of  Laying  Out  Circular  Curves  for  Railroads. 

i2mo,  morocco,  2  50 

Cross-section  Sheet Paper,  23 

Webb's  Railroad  Construction i6mo,  morocco,  5  oo 

Economics  of  Railroad  Construction , Large  12010,  2  50 

Wellington's  Economic  Theory  of  the  Location  of  Railways.      ....  Small  8vo.  5  oo 


DRAWING. 

Barr's  Kinematics  of  Machinery 8vo  2  50 

*  Bartlett's  Mechanical  Drawing 8vo,  3  oo 

*  "  "  "         Abridged  Ed 8vo,  150 

Coolidge's  Manual  of  Drawing 8vo,  paper,  i  oo 

9 


Coolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  Engi- 
neers  Oblong  4to,  2  50 

Durley's  Kinematics  of  Machines 8vo,  4  oo 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications 8vo,  2  ZQ. 

Hill's  Text-book  on  Shades  and  Shadows,  and  Perspective STO,  2  oo 

Jamison's  Elements  of  Mechanical  Drawing 8vo,  2  50 

Advanced  Mechanical  Drawing 8vo,  2  oo 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery 8vo,  i  50 

Part  n.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

MacCord's  Elements  of  Descriptive  Geometry 8vo,  3  oo 

Kinematics;  or,  Practical  Mechanism 8vo,  5  oo 

Mechanical  Drawing 4to,  4  oo 

Velocity  Diagrams 8vo,  i  50 

MacLeod's  Descriptive  Geometry Small  8vo,  i  50 

*  Mahan's  Descriptive  Geometry  and  Stone-cutting 8vo,  i  50 

Industrial  Drawing.     (Thompson.) 8vo,  3  50 

Meyer's  Descriptive  Geometry 8vo,  2  oo 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (R.  S.)  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

Smith  (A.  W.)  and  Marx's  iTachine  Design 8vo,  3  oo 


*  Titsworth's  Elements  of  Mechanical  Drawing Oblong  8vo, 

Warren's  Elements  of  Plane  and  Solid  Free-hand  Geometrical  Drawing.  i2mo, 

Drafting  Instruments  and  Operations i2mo, 

Manual  of  Elementary  Projection  Drawing 12 mo, 

Manual  of  Elementary  Problems  in  the  Linear  Perspective  of  Form  and 

Shadow i2mo, 

Plane  Problems  in  Elementary  Geometry i2mo, 


25 
00 
25 

50 

00 

25 

Primary  Geometry i2mo,  75 

Elements  of  Descriptive  Geometry,  Shadows,  and  Perspective 8vo,  -3  50 

General  Problems  of  Shades  and  Shadows 8vo,  3  oo 

Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

Problems,  Theorems,  and  Examples  in  Descriptive  Geometry 8vo,  2  50 

Weisbach's    Kinematics    and    Power    of    Transmission.        (Hermann    and 

Klein.) 8vo,  5  oo 

Whelpley's  Practical  Instruction  in  the  Art  of  Letter  Engraving i2mo,  2  oo 

Wilson's  (H.  M.)  Topographic  Surveying 8vo,  3  50 

Wilson's  (V.  T.)  Free-hand  Perspective 8vo,  2  50 

Wilson's  (V.  T.)  Free-hand  Lettering .8vo,  i  oo 

Woolf's  Elementary  Course  in  Descriptive  Geometry Large  8vo,  3  oo 


ELECTRICITY  AND  PHYSICS. 

Anthony  and  Brackett's  Text-book  of  Physics.     (Magie.) Small  8vo,  3  oo 

Anthony's  Lecture-notes  on  the  Theory  of  Electrical  Measurements.  .  .  .  I2mo,  i  oo 

Benjamin's  History  of  Electricity 8vo,  3  oo 

Voltaic  Cell 8vo,  3  oo 

Classen's  Quantitative  Chemical  Analysis  by  Electrolysis.     (Boltwood.).8vo,  3  oo 

*  Collins's  Manual  of  Wireless  Telegraphy i2mo,  i  50 

Morocco,  2  oo 

Crehore  and  Squier's  Polarizing  Photo-chronograph.  .     8vo,  3  oo 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  i6mo,  morocco,  5  oo 

10 


Dolezalek's    Theory   of   the    Lead   Accumulator    (Storage    Battery).      (Von 

Ende.) i2mo,  2  50 

Duhera's  Thermodynamics  and  Chemistry.     (Burgess.) 8vo,  4  oo 

Flather's  Dynamometers,  and  the  Measurement  of  Power 12 mo,  3  oo 

Gilbert's  De  Magnete.     (Mottelay.) 8vo,  2  50 

Hanchett's  Alternating  Currents  Explained 121110,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Holman's  Precision  of  Measurements 8vo,  2  oo 

Telescopic   Mirror-scale  Method,  Adjustments,  and   Tests.  . .  .Large  8vo,  75 

Kinzbrunner's  Testing  of  Continuous-current  Machines 8vo,  2  oo 

Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

Le  Chatelier  s  High-temperature  Measurements.  (Boudouard — Burgess.)  I2mo,  3  oo 

Lob's  Electrochemistry  of  Organic  Compounds.     (Lorenz.) 8vo,  3  oo 

*  Lyons'?  Treatise  on  Electromagnetic  Phenomena.   Vols.  I.  and  II.  8vo,  each,  6  oo 

*  Michie's  Elements  of  Wave  Motion  Relating  to  Sound  and  Light 8vo,  4  oo 

Niaudet's  Elementary  Treatise  on  Electric  Batteries.     (Fishback.) i2mo,  2  50 

*  Parshall  and  Hobart's  Electric  Machine  Design 4to,  half  morocco,  12  50 

*  Rosenberg's  Electrical  Engineering.     (Haldane  Gee — Kinzbrunner.).  .  .8vo, 


Ryan,  Norris,  and  Hoxie's  Electrical  Machinery.     Vol.  1 8vo, 

Thurston's  Stationary  Steam-engines 8vo, 

*  Tillman's  Elementary  Lessons  in  Heat ,. 8vo, 

Tory  and  Pitcher's  Manual  of  Laboratory  Physics Small  8vo, 

Hike's  Modern  Electrolytic  Copper  Refining 8vo,    3  oo 


LAW. 

*  Davis's  Elements  of  Law 8vo,  2  50 

*  Treatise  on  the  Military  Law  of  United  States 8vo,  7  oo 

*  Sheep,  7  50 

Manual  for  Courts-martial i6mo,  morocco,  i  50 

Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  oo 

Sheep,  6  50 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  Svo,  5  oo 

Sheep,  5  50 

Law  of  Contracts 8vo,  3  oo 

Winthrop's  Abridgment  of  Military  Law I2mo,  2  50 


MANUFACTURES. 

Bernadou's  Smokeless  Powder — Nitre-cellulose  and  Theory  of  the  Cellulose 

Molecule 1 21110 ,  2  50 

Bolland's  Iron  Founder I2mo,  2  50 

The  Iron  Founder,"  Supplement i2mo,  2  50 

Encyclopedia  of  Founding  and  Dictionary  of  Foundry  Terms  Used  in  the 

Practice  of  Moulding 12010,  3  oo 

Claassen's  Beet-sugar  Manufacture.    (Hall  and  Rolfe.) 8vo,  3  oo 

*  Eckel's  Cements,  Limes,  and  Plasters 8vo,  6  oo 

Eissler's  Modern  High  Explosives 8vo,  4  oo 

Effront's  Enzymes  and  their  Applications.     (Prescott.) 8vo,  3  oo 

Fitzgerald's  Boston  Machinist 121110,  i  oo 

Ford's  Boiler  Making  for  Boiler  Makers i8mo,  i  oo 

Hopkin's  Oil-chemists'  Handbook 8vo,  3  oo 

Keep's  Cast  Iron 8vo,  2  50 

11 


Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control Large  8vo,  7  50 

*  McKay  and  Larsen's  Principles  and  Practice  of  Butter-making 8vo,  i  50 

Matthews's  The  Textile  Fibres 8vo,  3  50 

Metcalf's  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Metcalfe's  Cost  of  Manufactures — And  the  Administration  of  Workshops. 8vo,  5  oo 

Meyer's  Modern  Locomotive  Construction 4to,  10  oo 

Morse's  Calculations  used  in  Cane-sugar  Factories i6mo,  morocco,  i  50 

*  Reisig's  Guide  to  Piece-dyeing 8vo,  25  oo 

Rice's  Concrete-block  Manufacture 8vo,  2  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Smith's  Press-working  of  Metals 8vo,  3  oo 

Spalding's  Hydraulic  Cement i2mo,  2  oo 

Spencer's  Handbook  for  Chemists  of  Beet-sugar  Houses i6mo,  morocco,  3  oo 

Handbook  for  Cane  Sugar  Manufacturers »6mo,  morocco,  3  oo 

Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced 8vo,  5  oo 

Thurston's  Manual  of  Steam-boilers,  their  Designs,  Construction  and  Opera- 
tion  8vo,  5  oo 

*  Walke's  Lectures  on  Explosives 8vo,  4  oo 

Ware's  Beet-sugar  Manufacture  and  Refining Small  8vo,  4  oo 

Weaver's  Military  Explosives 8vo,  3  oo 

West's  American  Foundry  Practice i2mo,  2  50 

Moulder's  Text-book i2mo,  2  50 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Rustless  Coatings:   Corrosion  and  Electrolysis  of  Iron  and  Steel.  .8vo,  4  oo 


MATHEMATICS. 

Baker's  Elliptic  Functions 8vo,    i  50 

Elements  of  Differential  Calculus i2mo,    4  oo 

oo 

50 
50 
50 
25 
50 
75 
50 
Rational  Geometry i2mo,  75 

*  Johnson's  (J.  B.)  Three-place  Logarithmic  Tables:   Vest-pocket  size. paper,        15 

100  copies  for    5  oo 

*  Mounted  on  heavy  cardboard,  8  X  10  inches,        25 

10  copies  for    2  oo 
Johnson's  (W   W.)  Elementary  Treatise  on  Differential  Calculus.  .Small  8vo,    3  oo 

Elementary  Treatise  on  the  Integral  Calculus Small  8vo,     i  50 

Johnson's  (W.  W.)  Curve  Tracing  in  Cartesian  Co-ordinates i2mo,     i  oo 

Johnson's  (W.  W.)  Treatise  on  Ordinary  and  Partial  Differential  Equations. 

Small  8vo,    3  50 
Johnson's  (W.  W.)  Theory  of  Errors  and  the  Method  of  Least  Squares.  i2mo,     i  50 

*  Johnson's  (W  W.)  Theoretical  Mechanics i2mo,    3  oo 

Laplace's  Philosophical  Essay  on  Probabilities.     (Truscott  and  Emory.).  i2mo,    2  oo 

*  Ludlow  and  Bass.     Elements  of  Trigonometry  and  Logarithmic  and  Other 

Tables 8vot    3  oo 

Trigonometry  and  Tables  published  separately Each,    2  oo 

*  Ludlow's  Logarithmic  and  Trigonometric  Tables 8vo.    i  oo 

Manning's  Irrational  Numbers  and  their  Representation  by  Sequences  and  Series 

Tamo      i  25 

12 


Briggs's  Elements  of  Plane  Analytic  Geometry i2mo, 

Compton's  Manual  of  Logarithmic  Computations i2mo, 

Davis's  Introduction  to  the  Logic  of  Algebra 8vo, 

*  Dickson's  College  Algebra Large  i2mo, 

*  Introduction  to  the  Theory  of  Algebraic  Equations Large  i2mo, 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications 8vo, 

Halsted's  Elements  of  Geometry 8vo, 

Elementary  Synthetic  Geometry 8vo, 


Mathematical  Monographs.     Edited  by  Mansfield  Merriman  and  Robert 

S.  Woodward Octavo,  each    i  oo 

No.  i.  History  of  Modern  Mathematics,  by  David  Eugene  Smith. 
No.  2.  Synthetic  Projective  Geometry,  by  George  Bruce  Halsted. 
No.  3.  Determinants,  by  Laenas  Gifford  Weld.  No.  4.  Hyper- 
bolic Functions,  by  James  McMahon.  No.  5.  Harmonic  Func- 
tions, by  William  E.  Byerly.  No.  6.  Grassmann's  Space  Analysis, 
by  Edward  W.  Hyde.  No.  7.  Probability  and  Theory  of  Errors, 
by  Robert  S.  Woodward.  No.  8.  Vector  Analysis  and  Quaternions, 
by  Alexander  Macfarlane.  No.  9.  Differential  Equations,  by 
William  Woolsey  Johnson.  No.  10.  The  Solution  of  Equations, 
by  Mansfield  Merriman.  No.  n.  Functions  of  a  Complex  Variable, 
by  Thomas  S.  Fiske. 

Maurer's  Technical  Mechanics.  .  . 8vo,    4  oo 

Merriman's  Method  of  Least  Squares 8vo,    2  oo 

Rice  and  Johnson's  Elementary  Treatise  on  the  Differential  Calculus. .  Sm.  8vo,    3  oo 

Differential  and  Integral  Calculus.     2  vols.  in  one Small  8vo,    2  50 

Wood's  Elements  of  Co-ordinate  Geometry 8vo,    2  oo 

Trigonometry:  Analytical,  Plane,  and  Spherical , i2mo,    i  oo 


MECHANICAL  ENGINEERING. 

MATERIALS  OF  ENGINEERING,  STEAM-ENGINES  AND  BOILERS. 

Bacon's  Forge  Practice i2mo,  i  50 

Baldwin's  Steam  Heating  for  Buildings I2mo,  2  50 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

*  Bartlett's  Mechanical  Drawing 8vo,  3  oo 

*  "  "  "        Abridged  Ed 8vo,  i  50 

Benjamin's  Wrinkles  and  Recipes I2mo,  2  oo 

Carpenter's  Experimental  Engineering 8vo,  6  oo 

Heating  and  Ventilating  Buildings 8vo,  4  oo 

Cary's  Smoke  Suppression  in  Plants  using  Bituminous  Coal.     (In  Prepara- 
tion.) 

Clerk's  Gas  and  Oil  Engine Small  8vo,  4  oo 

Coolidge's  Manual  of  Drawing 8vo,  paper,  i  oo 

Coolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  En- 
gineers   Oblong  4to,  2  50 

Cromwell's  Treatise  on  Toothed  Gearing i2mo,  i  50 

Treatise  on  Belts  and  Pulleys i2mo,  i  50 

Durley's  Kinematics  of  Machines f 8vo,  4  oo 

Flather's  Dynamometers  and  the  Measurement  of  Power i2mo,  3  oo 

Rope  Driving i2mo,  2  oo 

Gill's  Gas  and  Fuel  Analysis  for  Engineers i2mo,  i  25 

Hall's  Car  Lubrication. i2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Button's  The  Gas  Engine 8vo,  5  oo 

Jamison's  Mechanical  Drawing 8vo,  2  50 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

Kent's  Mechanical  Engineers'  Pocket-book i6mo,  morocco,  5  oo 

Kerr's  Power  and  Power  Transmission 8vo,  2  oo 

Leonard's  Machine  Shop,  Tools,  and  Methods 8vo,  4  oo 

*  Lorenz's  Modern  Refrigerating  Machinery.    (Pope,  Haven,  and  Dean.)  .  .  8vo,  4  oo 
MacCord's  Kinematics;  or  Practical  Mechanism 8vo,  5  oo 

Mechanical  Drawing 4to.  4  oo 

Velocity  Diagrams. 8vo,  i  50 

13 


MacFarland's  Standard  Reduction  Factors  for  Gases 8vo,  i  50 

Mahan's  Industrial  Drawing.     (Thompson.) 8vo,  3  50 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Richard's  Compressed  Air i2mo,  i  50 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  oo 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

Thurston's   Treatise   on   Friction  and   Lost   Work   in   Machinery   and   Mill 

Work..  . 8vo,  3  oo 

Animal  as  a  Machine  and  Prime  Motor,  and  the  Laws  of  Energetics .  12 mo,  i  oo 

Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  5°> 

Weisbach's    Kinematics    and    the    Power    of    Transmission.     (Herrmann — 

Klein.).  „ 8vo,  5  oo 

Machinery  of  Transmission  and  Governors.     (Herrmann — Klein.).  .8vo,  5  oo 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Turbines 8vo,  2  50 


MATERIALS   OP  ENGINEERING. 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering.    6th  Edition. 

Reset 8vo,  7  50 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Johnson's  Materials  of  Construction 8vo,  6  oo 

Keep's  Cast  Iron 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  50 

Martens's  Handbook  on  Testing  Materials.     (Henning.) 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

Strength  of  Material. i2mo,  i  oo 

Metcalf's  Steel.     A  man-a.  *cr  Steel-users i2mo,  2  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Smith's  Materials  of  Machines I2rno,  i  oo 

Thurston's  Materials  of  Engineering 3  vols.,  8vo,  8  oo 

Part  II.     Iron  and  Steel 8vo,  3  30 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Text-book  of  the  Materials  of  Construction 8vo,  5  oo 

Wood's  (De  V.)  Treatise  on  the  Resistance  of  Materials  and  an  Appendix  on 

the  Preservation  of  Timber ! 8vo,  2  oo 

Elements  of  Analytical  Mechanics 8vo,  3  oo 

Wood's  (M.  P.)  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel..                                                 8vo,  400 


STEAM-ENGINES  AND  BOILERS. 

Berry's  Temperature-entropy  Diagram i2mo,  i  25 

Carnot's  Reflections  on  the  Motive  Power  of  Heat.     (Thurston.).  ,  .     ..i2mo,  150 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  .  .  .i6mo  mor.,  5  oo 

Ford's  Boiler  Making  for  Boiler  Makers i8mo,  i  oo 

Goss's  Locomotive  Sparks 8vo,  2  oo 

Hemenway's  Indicator  Practice  and  Steam-engine  Economy i2mo,  2  oo 

14 


Button's  Mechanical  Engineering  of  Power  Plants. 8vo,  5  oo 

Heat  and  Heat-engines 8vo.  5  oo 

Kent's  Steam  boiler  Economy 8vo,  4  oo 

Kneass's  Practice  and  Theory  of  the  Injector 8vo,  i  50 

MacCord's  Slide-valves 8vo,  2  oo 

Meyer's  Modern  Locomotive  Construction 4to,  10  oo 

Peabody's  Manual  of  the  Steam-engine  Indicator f2mov  i  so 

Tables  of  the  Properties  of  Saturated  Steam  and  Other  Vapors 8vo,  i  oo 

Thermodynamics  of  the  Steam-engine  and  Other  Heat-engines, 8vo,  5  oo 

Valve-gears  for  Steam-engines 8vo,  2  50 

Peabody  and  Miller's  Steam-boilers 8vo,  4  oo 

Pray's  Twenty  Years  with  the  Indicator Large  8vos  2  50 

Pupin's  Thermodynamics  of  Reversible  Cycles  in  Gases  and  Saturated  Vapors. 

(Osterberg.) ". I2mo,  i  25 

Reagan's  Locomotives:  Simple   Compound,  and  Electric i2mo,  2  50 

Rontgen's  Principles  of  Thermodynamics.     (Du  Bois.) 8vo,  5  oo> 

Sinclair's  Locomotive  Engine  Running  and  Management i2mo,  2  oo 

Smart's  Handbook  of  Engineering  Laboratory  Practice i2mo,  2  50 

Snow's  Steam-boiler  Practice. 8vo,  3  oo 

Spangler's  Valve-gears .8vo,  2  50 

Notes  on  Thermodynamics I2mo,  i  oo 

Spangler,  Greene,  and  Marshall's  Elements  of  Steam-engineering 8vo,  3  oo 

Thomas's  Steam-turbines «, 8vo,  3  50 

Thurston's  Handy  Tables 8vo,  i  50 

Manual  of  the  Steam-engine 2  vols.,  8vo,  10  oo 

Part  I.     History,  Structure,  and  Theory.  .  ; 8vo,  6  oo 

Part  II.     Design,  Construction,  and  Operation 8vo,  6  oo 

Handbook  of  Engine  and  Boiler  Trials,  and  the  Use  of  the  Indicator  and 

the  Prony  Brake 8vo,  5  oo 

Stationary  Steam-engines 8vo,  2  50 

Steam-boiler  Explosions  in  Theory  and  in  Practice i2mo,  i  50 

Manual  of  Steam-boilers,  their  Designs,  Construction,  and  Operation 8vo,  5  oo 

Wehrenf  enning's  Analysis  and  Softening  of  Boiler  Feed-water  (Patterson)  8vo,  4  oo 

Weisbach's  Heat,  Steam,  and  Steam-engines.     (Du  Bois.) 8vo,  5  oo 

Whitham's  Steam-engine  Design 8vo,  5  oo 

Wood's  Thermodynamics,  Heat  Motors,  and  Refrigerating  Machines.  .  .8vo,  4  oo 


MECHANICS  AND  MACHINERY. 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures   8vo,  7  50 

Chase's  The  Art  of  Pattern-making i2mo,  2  50 

Church's  Mechanics  of  Engineering 8vo,  6  oo 


Notes  and  Examples  in  Mechanics 8vo, 

Compton's  First  Lessons  in  Metal-working i2mo, 

Compton  and  De  Groodt's  The  Speed  Lathe i2mo, 

Cromwell's  Treatise  on  Toothed  Gearing i2mo, 

Treatise  on  Belts  and  Pulleys i2mo, 

Dana's  Text-book  of  Elementary  Mechanics  for  Colleges  and  Schools.  .i2mo, 


oo 
50 
50 
50 
50 
So 

Dingey's  Machinery  Pattern  Making i2mo,    2  oo 

Dredge's  Record  of  the  Transportation  Exhibits  Building  of  the  World's 

Columbian  Exposition  of  1893. 4to  half  morocco,    5  oo 

u  Bois's  Elementary  Principles  of  Mechanics; 

Vol.      I.     Kinematics 8vo,    3  50 

VoL    II.     Statics 8vo,    4  oo 

Mechanics  of  Engineering,     Vol.    I Small  4to,    7  50 

Vol.  II Small  4to,  10  oo 

Durley's  Kinematics  of  Machines.  ,    .    8vo,    4  oo 

15 


Fitzgerald's  Boston  Machinist i6mo,  i  oo 

Flather's  Dynamometers,  and  the  Measurement  of  Power tamo,  3  oo 

Rope  Driving i2mo,  2  oo 

Goss's  Locomotive  Sparks 8vo,  2  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Hall's  Car  Lubrication i2mo,  i  oo 

Holly's  Art  of  Saw  Filing i8mo,  75 

James's  Kinematics  of  a  Point  and  the  Rational  Mechanics  of  a  Particle. 

Small  8vo,  2  oo 

*  Johnson's  (W,  W.)  Theoretical  Mechanics i2mo,  3  o<> 

Johnson's  (L.  J.)  Statics  by  Graphic  and  Algebraic  Methods. »  .  .  .8vo,  2  oo 

Jones's  Machine  Design: 

Part    I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts.  ; .  .-** 8vo,  3  oo 

Kerr's  Power  and  Power  Transmission 8vo,  2  oo 

Lanza's  Applied  Mechanics 8vo,  7  50 

Leonard's  Machine  Shop,  Tools,  and  Methods 8vo,  4  oo 

*  Lorenz's  Modern  Refrigerating  Machinery.     (Pope,  Haven,  and  Dean.). 8vo,  4  oo 
MacCord's  Kinematics;  or.  Practical  Mechanism 8vo,  5  oo 

Velocity  Diagrams.  , .  t 8vo,  i  50 

*  Martin's  Text  Book  on  Mechanics,  Vol.  I,  Statics 12010,  i  25 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merriman's  Mechanics  of  Materials - 8vo,  5  oo 

*  Elements  of  Mechanics i2mo,  i  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oo 

*  Parshall  and  Hobart's  Electric  Machine  Design 4to,  half  morocco,  12  50 

Reagan's  Locomotives:   Simple,  Compound,  and  Electric i2mo,  2  50 

Reid's  Course  in  Mechanical  Drawing. 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Richards's  Compressed  Air i2mo,  i  50 

Robinson's  Principles  of  Me'chanism 8vo,  3  oo 

Ryan,  Norris,  and  Hoxie's  Electrical  Machinery.     Vol.  1 8vo,  2  50 

Sanborn's  Mechanics :  Problems Large  i2mo,  i   50 

Schwamb  and  Merrill's  Elements  of  Mechanism. 8vo,  3  oo 

Sinclair's  Locomotive-engine  Running  and  Management i2mo,  2  oo 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  oo 

Smith's  (A.  W.)  Materials  of  Machines i2mo,  i  oo 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

Spanglar,  Greene,  and  Marshall's  Elements  of  Steam-engineering 8vo,  3  oo 

Thurston's  Treatise  on  Friction  and  Lost  Work  in    Machinery  and    Mill 

Work 8vo,  3  oo 

Animal  as  a  Machine  and  Prime  Motor,  and  the  Laws  of  Energetics.  i2mo,  i  oo 

Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

Weisbach's  Kinematics  and  Power  of  Transmission.   (Herrmann — Klein. ) .  8vo ,  5  oo 

Machinery  of  Transmission  and  Governors.      (Herrmann — Klein.). 8vo,  5  oo 

Wood's  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Principles  of  Elementary  Mechanics i2mo,  i  25 

Turbines 8vo,  2  50 

The  World's  Columbian  Exposition  of  1893  ... 4to,  ^  i  oo 


METALLURGY. 

Egleston's  Metallurgy  of  Silver,  Gold,  and  Mercury- 

Vol.    I.     Silver.  .  . 8vo,  7  BO 

Vol.  II.     Gold  and  Mercury. .  „  . 8vo,  7  50 

Goesel's  Minerals  and  Metals:     A  Reference  Book ; .  .  .  .  i6mo,  mor.  3  oo 

**  Iles's  Lead-smelting.     (Postage  9  cents  additional.). i2mo,  2  50 

Keep's  Cast  Iron 8vo,  2  50 

16 


Kunhardt's  Practice  of  Ore  Dressing  in  Europe. 8vo,  i  50 

Le  Chatelier's  High-temperature  Measurements.  (Boudouard — Burgess.)i2mo.  3  oo 

Metcalf' s  Steel.     A  Manual  for  Steel-users i2rno,  2  oo 

Miller's  Cyanide  Process i2mo,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.). . .  .  i2mo,  2  -50 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Smith's  Materials  of  Machines I2mo,  i  oo 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  oo 

Part    II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  oo 


t 
MINERALOGY. 

Barringer's  Description  of  Minerals  of  Commercial  Value.    Oblong,  morocco,  2  50 

Boyd's  Resources  of  Southwest  Virginia 8vo,  3  oo 

Map  of  Southwest  Virignia Pocket-book  form.  2  oo. 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.).  .  . 8vo,  4  oo 

Chester's  Catalogue  of  Minerals 8vo,  paper,  i  oo 

Cloth,  i  25 

Dictionary  of  the  Names  of  Minerals ' 8vo  3  50 

Dana's  System  of  Mineralogy Large  8vo,  half  leather    12  50 

First  Appendix  to  Dana's  New  "  System  of  Mineralogy." Large  8vo,  i  oo 

Text-book  of  Mineralogy 8vo,  4  oo 

Minerals  and  How  to  Study  Them I2mo,  i  50 

Catalogue  of  American  Localities  of  Minerals Large  8vo,  i  oo 

Manual  of  Mineralogy  and  Petrography i2mo,  2  oo 

Douglas's  Untechnical  Addresses  on  Technical  Subjects i2mo,  i  oo 

Eakle's  Mineral  Tables 8vo,  i  25 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Goesel's  Minerals  and  Metals:     A  Referente  Book i6mo,  mor..  3  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) I2mo,  i  25 

Hussak's  The  Determination  of  Rock-forming  Minerals.    ( Smith.). Small  8vo,  2  oo 

Merrill's  Non-metallic  Minerals-   Their  Occurrence  and  Uses 8vo,  4  oo 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

8vo,  paper,  50 
Rosenbusch's   Microscopical   Physiography   of   the   Rock-making  Minerals. 

(Iddings.) 8vo,  5  oo 

*  Tillman's  Text-book  of  Important  Minerals  and  Rocks 8vo,  2  oo 


MINING. 

Beard's  Ventilation  of  Mines 12010,  2  50 

Boyd's  Resources  of  Southwest  Virginia.  . 8vo,  3  oo 

Map  of  Southwest  Virginia. , Pocket-book  form,  2  oo 

Douglas's  Untechnical  Addresses  on  Technical  Subjects i2mo,  i  oo 

*  Drinker's  Tunneling,  Explosive  Compounds*  and  Rock  Drills.  . 4to,hf.  inor.,  25  oo 

Eissler's  Modern  High  Explosives 8  -->  4   -& 

Gaesel's  Minerals  and  Metals  •     A  Reference  Book i6mo,  mor.  3  oo 

Goodyear's  Coal-mines  of  the  Western  Coast  of  the  United  States i2mo,  2  50 

Ihlseng's  Manual  of  Mining 8vo,  5  oo 

**  Iles's  Lead-smelting.     (Postage  QC.  additional.) i2mo,  2  50 

Kunhardt's  Practice  of  Ore  Dressing  in  Europe.  .      8vo,  i  50 

Miller's  Cyanide  Process i2mo,  i  oo 

17 


O'DriscolTs  Notes  on  the  Treatment  of  Gold  Ores Svo,  2  oo 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

*  Walke's  Lectures  on  Explosives ~ 8vo,  4  oo 

Weaver's  Military  Explosives 8vo,  3  oo 

Wilson's  Cyanide  Processes . i2tno,  i  50 

Chlorination  Process lamo,  i  50 

Hydraulic  and  Placer  Mining I2mo,  2  oo 

Treatise  on  Practical  and  Theoretical  Mine  Ventilation T2mo,  125 


SANITARY  SCIENCE. 

Bashore's  Sanitation  of  a  Country  House i2mo,  i  oo 

*  Outlines  of  Practical  Sanitation I2mo,  i  25 

FolwelTs  Sewerage.     (Designing,  Construction,  and  Maintenance.) 8vo,  3  oo 

Water-supply  Engineering .•  .8vo,  4  oo 

Fowler's  Sewage  Works  Analyses I2mo,  2  oo 

Fuertes's  Water  and  Public  Health i2mo,  i  50 

Water-filtration  Works i2mo,  2  50 

Gerhard's  Guide  to  Sanitary  House-inspection i6mo,  i  oo 

Goodrich's  Economic  Disposal  of  Town's  Refuse Demy  8vo,  3  50 

Hazen's  Filtration  of  Public  Water-supplies .8vo,  3  oo 

Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control 8vo,  7  50 

Mason's  Water-supply.  (Considered  principally  from  a  Sanitary  Standpoint)  8vo,  4  oo 

Examination  of  Water.     (Chemical  and  Bacteriological.) i2mo,  i  25 

Ogden's  Sewer  Design i2mo,  2  oo 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis 12010,  i  25 

*  Price's  Handbook  on  Sanitation. i2mo,  i  50 

Richards's  Cost  of  Food.     A  Study  in  Dietaries i2mo,  i  oo 

Costiof  Living  as  Modified  by  Sanitary  Science i2mo,  i  oc 

Cost  of  Shelter i2mo,  i  oo 

Richards  and  Woodman's  Air,  Water,  and  Food  from  a  Sanitary  Stand- 
point  8vo,  2  oo 

*  Richards  and  Williams's  The  Dietary  Computer 8vo,  i  50 

Rideal's  Sewage  and  Bacterial  Purification  of  Sewage 8vo,  3  50 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) i2mo,  i  oo 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo,  7  50 

Woodhull's  Notes  on  Military  Hygiene i6mo,  i  5J 

*  Personal  Hygiene izmo,  i  oo 


MISCELLANEOUS. 

De  Fursac's  Manual  of  Psychiatry.     (Rosanoff  and  Collins.).  ..  .Large  i2mo,  2  50 

Ehrlich's  Collected  Studies  on  Immunity  ( Bolduan) 8vo,  C  oo 

Emmons's  Geological  Guide-book  of  the  Rocky  Mountain  Excursion  of  the 

International  Congress  of  Geologists Large  Svo,  i  50 

Ferrel's  Popular  Treatise  on  the  Winds Svo,  4  oo 

Haines's  American  Railway  Management i2mo,  2  50 

Mott's  Fallacy  of  the  Present  Theory  of  Sound i6mo,  i  oo 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute,  1824-1894.. Small  Svo,  3  oo 

Rostoski's  Serum  Diagnosis.     (Bolduan.) i2mo  i  oo 

Rother ham's  Emphasized  New  Testament c Large  Svo,  3  oo 

18 


Steel's  Treatise  on  the  Diseases  of  the  Dog 8vo,  3  50 

The  World's  Columbian  Exposition  of  1893 4to,  i  oo 

Von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) i2mo,  i  oo 

Winslow's  Elements  of  Applied  Microscopy I2mo,  i  50 

Worcester  and  Atkinson.     Small  Hospitals,  Establishment  and  Maintenance; 

SuggestionsforHospitalArchitecture:PlansforSmallHospital.i2mo,  i  25 


HEBREW  AND  CHALDEE  TEXT-BOOKS. 


Green's  Elementary  Hebrew  Grammar I2mo,  i  25 

Hebrew  Chrestomathy 8vo,  2  oo 

Gesenius's  Hebrew  and  Chaldee  Lexicon  to  the  Old  Testament  Scriptures. 

(Tregelles.) Small  4to,  half  morocco,  5  oo 

Letteris's  Hebrew  Bible , 8vo,  2  25 

19 


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